Essays on the floating-matter of the air in relation to putrefaction and infection
SS x \ ANS \\\ AN eS RS UUUUU! <* UUUU ‘oA 7. mi Ue - To JUUUUY ine JU q =f Eo } ) Gornell University Library Ithaca, New York j GEORGE FRANCIS ATKINSON BOTANICAL LIBRARY 1920 Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http :/Awww.archive.org/details/cu31924003516923 PUTREFACTION AND INFECTION. PROFESSOR JOHN TYNDALL'S WORKS. Essays on the Floating Matter of the Air, in Relation to Putrefaction and Infection. 12mo. Cloth, $1.50. On Forms of Water, in Clouds, Rivers, Ice, and Gla- ciers. With 85 Illustrations, 12mo. Cloth, $1.50. Heat as a Mode of Motion. New edition. 12mo. loth, $2.50. On Sound; A Course of Eight Lectures delivered at the Royal Institution of Great Britain. Illustrated. 12mo. New edition. Cloth, $2.00. Fragments of Science for Unscientific People. 12mo. ew revised and enlarged edition. Cloth, $2.50. Light and Electricity. 12mo. Cloth, $1.25. Lessons in Electricity, 1715-16. 12mo. Cloth, $1.00. Hours of Exercise in the Alps. With Illustrations. 12mo. Cloth, $2.C0. a rs as @ Discoverer. A Memoir. 12mo. Cloth, Contributions to Molecular Physics in the Domain of Radiant Heat. $5.00. Six Lectures on Light. Delivered in America in 187278. With an Appendix and numerous Illus- trations. Cloth, $1.50. Farewell cif ha given to Professor Tyndall, at Del- monico’s, New York, February 4, 1878. Paper, 50 cents. Address delivered before the British Association, assembled at Belfast. Revised, with Additions, by the author, since the Delivery. 12mo. Paper, 50 cents. New York: D. Arrieton & Co., 1, 8, & 5 Bond St. ESSAYS ON THE FLOATING-MATTER OF THE AIR IN RELATION TO PUTREFACTION AND INFECTION. BY JOHN TYNDALL, F.R.S. (M.D. TUBINGEN). NEW YORK: D. APPLETON AND COMPANY, 1, 8, any 5 BOND STREET 1884. INTRODUCTORY NOTE. _— THE VIRTUAL TRIUMPH of the Antiseptic system of surgery, based as that system is on the recognition of living contagia as the agents of putrefaction, is of good augury as regards the receptivity of the public mind to new views respecting the nature of contagia generally. To the credit of English surgeons it stands recorded that, guided by their practical sagacity, they had adopted in their hospitals measures of amelioration which reduced, almost to a minimum, the rate of mor- tality arising from the ‘mortification’ of wounds. They had discovered the evils incident to ‘ dirt;’ and, by keeping dirt far away from them, they had saved innumerable lives, which would undoubtedly have suc- cumbed under conditions prevalent in many of the hospitals of continental Europe. In thus acting, English surgeons were, for the most part, ‘ wiser than they knew.’ Their knowledge, how- ever momentous in its practical applications, was still empirical knowledge. That dirt was fatal they had discovered ; but why it was fatal few of them knew. viii INTRODUCTORY NOTE. At this point Lister came forward with a scientific principle which rendered all plain. Dirt was fatal, not as dirt, but because it contained living germs which, as Schwann was the first to prove, are the cause of putrefaction. Lister extended the generalization of Schwann from dead matter to living matter, and by this apparently simple step revolutionized the art of surgery. He changed it, in fact, from an art into a science. ‘Listerism’ is sometimes spoken of as if it merely consisted in the application of carbolic acid spray; but no man of any breadth of vision will regard the subject thus. The antiseptic system had been enun- ciated, expounded, and illustrated, prior to the intro- duction of the spray. The spray is a mere offshoot of the system—elegant and effective it is true, but still a matter of detail. In company with my excellent friend Mr. John Simon, I once visited St. Bar- tholomew’s Hospital, and became acquainted, in its wards, with the practice of the late Mr. Callender. The antiseptic system was there as stringently applied as at King’s College. Immediately before his departure to America I spoke to Mr. Callender on this subject ; and he then told me expressly, that his aim and hope had been, not to introduce a new principle, but to simplify the methods of Lister. And yet Mr. Callen- der’s practice is sometimes spoken of as if it were, in principle, different from that of his eminent contem- porary. It is interesting, and indeed pathetic, to observe how long a discovery of priceless value to humanity INTRODUCTORY NOTE. ix may be hidden away, or rather lie openly revealed, before the final and apparently obvious step is taken towards its practical application. In 1837, Schwann clearly established the connexion between putrefaction and microscopic life; but thirty years had to elapse before Lister extended to wounds the researches of Schwann on dead flesh and animal infusions. Prior to Lister the possibility of some such extension had occurred to other minds. Penetrative men had seen that the germs which produce the putrefaction of meat might also act with fatal effect in the wards of a hospital. Thus, for example, in a paper read before the British Medical Association at Cambridge in 1864, Mr. Spencer Wells pointed out that the experiments of Pasteur, then recent, had ‘all a very important bearing upon the development of purulent infection, and the whole class of diseases most fatal in hospitals and other over- crowded places.’ Mr. Wells did not, as far as I know, introduce any systematic mode of combating the organ- isms whose power he so early recognised. But, I believe, in hardly any other department of surgery has the success of the antiseptic system been more con- spicuous and complete than in that particular sphere of practice in which Mr. Wells has won so great a name. A remark in the paper just referred to would seem to indicate that, in regard to the further possible influence of germs, the thoughts of Mr. Spencer Wells had passed beyond the bounds of pure surgical -prac- tice. ‘Their influence,’ he says, ‘ on the propagation of x INTRODUCTORY NOTE. epidemic and contagious diseases has yet to be made out.’ This shows that at the time here referred to the Germ Theory, in its wider medical sense, had begun to ferment in England. Two years, indeed, prior to the above occasion, and for the use of the same Association as that addressed by Mr. Wells, the late Dr. William Budd had drawn up a series of ‘Suggestions towards a Scheme for the Investigation of Epidemic and Epizootic Diseases,’ which strikingly illustrate the insight of a moan of genius, withdrawn from the stimulus of the metropolis, and working alone, at a time when the whole medical profession in England entertained views opposed to his. Budd states in succession, and with perfect clearness, the points which he considers most worthy of the attention of the Association. He re- commends inquiry as to the nature of the evidence alleged to prove the disease under investigation to be contagious or communicable. Whether such disease admits of being artificially propagated by inoculation or otherwise. Through what surface or surfaces the virus may be shown to enter the body, and to leave it, when the disease is taken in the natural way. Whether the disease is distinguished by eruptions external or internal. Whether it has a period of true incubation; and if so, what are the length and limits of that period. Whether one attack, as in smallpox and many other contagious diseases, preserves against future attacks. Whether in the case of human disease animals as well as man are susceptible, and if so, what animals. What, is the evidence, if any, as to the particular country or region in which the disease first appeared. What are INTRODUCTORY NOTE. xi its present geographical limits. Whether there is any evidence of its modern or recent introduction into countries previously exempt. How far any such disease may have been prevented from invading new countries, or from spreading from any particular centre, by measures directed against contagion. Above all, to determine what is the nature, and what the true value, of the evidence supposed to show that the specific poison of a contagious disease may originate spon- taneously, or be generated de novo. ‘What we most want to know,’ adds Budd, ‘in regard to this whole group of diseases is, where, and how, the specific poisons which cause them, breed and multiply,’ Budd’s own relation to the question here raised was distinct and, under the circumstances, impressive. ‘ After giving many years of time and thought to an examination of the evidence bearing on. this question,’ he comes to the conclusion ‘that there is no proof whatever’ that the poisons of specific contagious diseases ever originate spontaneously. ‘That the evidence on which the contrary conclusion is founded is negative only; that evidence of precisely the same order, only to all appeararice still more cogent, would prove animals and plants, even of large species, to originate spontaneously; that this evidence is therefore of no weight ; and, lastly, that all the really important facts point the other way, and tend to prove that these poisons (to use a term which is probably provisional only), like animals and plants, however they may have once originated, are only propagated now by the law of continuous succession.’ xii INTRODUCTORY NOTE. The word ‘ poisons,’ here provisionally employed, was a concession on Budd’s part to his weaker brethren ; for he, without a shade of doubt, considered the poison to be a real living seed. There was, I believe, but one physician of eminence in England who, at the time here referred to, shared this conviction, and who im- parted to Budd the incalculable force derived from the approbation and encouragement of a wise and cele- brated man. It gives me singular pleasure to write down here the name of the venerable Sir Thomas Watson, who lent to William Budd unfailing counte- nance and support, and who has lived to see that the views which commended themselves to his philosophic judgment are at the present moment advancing with resistless momentum among the members of the medical profession. It was far otherwise at the time to which we here refer. ‘Opinions like these,’ said Budd, ‘are no doubt, at present, those of a small minority. A very large, and by far the most influential school in this country—a school which probably embraces the great majority of medical practitioners, and the whole of the “sanitary public”—holds the exact contrary; and teaches that sundry of these poisons are constantly being generated de novo by the material conditions which surround us.’ Budd’s remark regarding the spontaneous generation of ‘animals and plants, even of large species,’ is both pregnant and pertinent. In reference to special and solitary outbreaks of contagious fever, I have frequently heard physicians of distinction affirm, without apparent misgiving, the ‘impossibility’ of importation from INTRODUCTORY NOTE. xiii without. On such occasions a reply, in the strict sense affirmed by William Budd, was always at hand; for I was able to adduce cases of solitary mushrooms, found upon out of the way Alpine slopes, to which the evidence would apply with greater force than to the cases on which the physicians referred to based their conclusions. With the atmosphere as a vehicle of universal intercommunication, it is hard to see any just warrant for the reliance of medical men upon the negative evidence stigmatized by Budd as valueless. It is, however, evidence by which many physicians are still influenced, and the effects of which it will probably require a generation of doctors, brought up under other conditions of culture and of practice, to wholly sweep away. These conditions are growing up around us, and their influence will be all-pervading before long. Never before was medicine manned and officered as it is now. To name here the workers at present engaged in the investigation of communicable diseases would be to extend beyond all reasonable limits this Introductory Note. On the old Baconian lines of observation and experiment the work is carried on. The intercommuni- cation of scientific thought plays here a most important part. It will probably have been noticed, that while physiologists and physicians in England and elsewhere were drawing copiously from the store of facts furnished by the researches of Pasteur, that admirable investigator long kept himself clear of physiology and medicine. There is, indeed, reason to believe that he was spurred on to his most recent achievements by the papers of xiv INTRODUCTORY NOTE. Burdon Sanderson, Koch, and others. The union of scientific minds is, or ought to be, organic. They are parts of the same body, in which every memter, under penalty of atrophy and decay, must discharge its due share of the duty imposed upon the whole. Of this ‘body,’ a short time since, England provided one of the healthiest limbs , but round that limb legislation has lately thrown a ligature, which threatens to damage its circulation and to divert its energies into foreign channels. In observational medicine one fine piece of work may be here referred to—the masterly inquiry of Dr. Thorne Thorne into the outbreak of typhoid fever at Caterham and Redhill. Hundreds were smitten by this epidemic, and many died. The qualities of mind illustrated in Dr. Thorne’s inquiry match those dis- played by William Budd in his memorable investigation of asimilar outbreak in Devonshire. Dr. Budd’s process was centrifugal—tracing from a single case in the village of North Tawton, the ravages of the fever far and wide. Dr. Thorne’s process was centripetal— tracing the epidemic backwards from the multitude of cases first: presented, to the single individual whose infected excreta, poured into the well at Caterham, were the cause of all. The Essays here presented to the reader belong to the A BC of the great subject touched upon in the foregoing Note. The two principal ones, namely, Essays II. and III., were prepared for the Royal Society, and are published in the ‘ Philosophical Trans- actions’ for 1876 and 1877. But, though written for INTRODUCTORY NOTE. xv that learned body, I sought to render their style and logic so clear as to render them accessible to any fairly cultivated mind. The Essays on ‘Fermentation’ and ‘Spontaneous Generation’ have already appeared else- where; while the first Essay, on ‘Dust and Disease, has been for some years before the public. It may be regarded as a kind of popular introduction to the more strenuous and original labours which follow it. The Essay most likely to try the reader’s patience is No. JII. On the whole, however, and particularly in its bearings on the Germ Theory of disease, it is probably the most important of all. The difficulties which sometimes beset the experimenter in these in- vestigations are best illustrated by this Essay. It shows, to my mind in a very impressive manner, the analogy of the spread of infection among organic in- fusions with its mode of propagation among human beings. The vital resistance of certain germs to heat is strikingly illustrated in the third Essay, one in- fusion being there proved to maintain its potentiality of life intact after eight hours’ continuous exposure to the temperature of boiling water. Under the plain guidance of the Germ Theory, it is however shown that an infusion of this stubborn character may be infallibly sterilized by discontinuous heating, in one hundredth part of the time requisite when the boiling is con- tinuous. Another question, to my mind of fundamental importance, is also disposed of in Essay III., where it is shown that the germs which exhibited the foregoing resistance are neither contained in the air, nor attached to the surface of the vessel, above the liquid, but that xvi INTRODUCTORY NOTE, they manifest their extraordinary vitality in the body of the liquid itself. On public sympathy the sanitary physician has mainly to rely for support, in a country where sanitary matters are left so much in the hands of the public itself as they are in England. But sympathy without cause—that is to say, without some basis of knowledge —is hardly to be expected. It is as a contribution to such knowledge that these Essays have been collected, and thrown into their present handy form. J. TYNDALL. Roya INSTITUTION: August 1881. CONTENTS. _—o——— ON DUST AND DISEASE. Experiments on Dusty Air : 5 . . .. The Germ Theory of Contagious Didensd . . oe Parasitic Diseases of Silkworms. Pasteur’s Researches ‘ ‘ Origin and Propagation of Contagious Matter . eo The Germ Theory applied to Surgery a . ‘ .. The Luminous Beam as a means of Research : A eas The Floating-Matter of the Air ‘ 3 . ‘ Dr. Bennett’s Experiments . . .. OPTICAL DEPORTMENT OF THE ATMOSPHERE IN RELATION TO PUTREFACTION AND INFEC- TION. § 1. Introduction : : : 2 : § 2. Method of Experiment ¢ : - : .. § 3. Deportment of Urine .  Haddock-Infusion . a : . 7 a § 7. Turnip-Infusion . 3 . ‘ 2 . 5 rae § 8. Hay-Infusion . : . : 7 . . :. § 9. Infusion of Sole . ¥ ‘ . ‘ : . ae § 10. Liver-Infusion . : . a 5 § 11. Infusions of Hare, Rabbit, Pheasant, and Grouse a § 12. Infusions of Codfish, Turbot, Herring, and Mullet. § 13. Infusions of Fowland Kidney . .. § 14. Boiling by an Internal Source of Heat . ‘ ‘ § 15. Partial Discussion of the Results. . .. xviii § 16. § 17. § 18. § 19. § 20. § 21. § 22. § 23. § 24. § 26. § 26. § 27. CONTENTS. Suspended Particles in Air and Water; their relation to Bacteria . ‘ : . . o 25 Recent Experiments on a Heterogenesis . .. Experiments with Filtered Air . : Experiments with Calcined Air. Infusions withdrawn from Air . . . F ae The Germ Theory of Contagious Disease es 2 ‘ Experiments with Hermetically-sealed Vessels . is Conditions as to the Temperature and Strength of In- fusions .. Developmental Power e Infusions ond Solutions : Air. germs contrasted with Water-germs c Diffusion of Germs in the Air. Tray of one hundred Tubes 3 Some Experiments of Pasteur and ther Relation to Bae- terial Clouds. Note I. Action of Basteria apoN a Beara of Light Note II. Fluorescence of Infusions . 2 FURTHER RESEARCHES ON THE DEPORTMENT AND Cr tr Lr > wm Murra Cr Lr eh er Mr rar VITALITY OF PUTREFACTIVE ORGANISMS. . Introduction . : é . - . Experiments of Pasteur, Roberts ait Cohn i. . Hay-Infusions. Preliminary Experiments with Pipette- bulbs . Hay-Infusions. Hepariments with Cohn’s Walbes z . Hay-Infusions (in Closed Chambers). . Desiccation of Germs. New Hay and old Hay-Infusions. Further Experiments with Closed Chambers . . . - :. . Experiments with Soaked Hay . Infusions of Fungi. . Infusions of Cucumber, Bectioot ie, : . New Experiments on Animal Infusions. Contradictory results . Infusions protected by ‘Glass Shades eontatning Ghlcinea, Air. F . Z :. . Further Precautions Gaalnet Tatestion, . Experiments in the Royal Gardens, Kew . Experiments on the Roof of the Royal Tdetitution. . Preliminary Experiments on the Resistance-limit of Germs to the temperature of Boiling Water 131 135 138 144 146 148 150 164 158 161 165 169 171 174 117 180 CONTENTS. xix § 17. Further Experiments on the Resistance-limit of Germs to the Boiling Temperature é 183 § 18. Change of Apparatus. New Hxperiments with Filtered Air . ;: : 188 § 19. Final proof that the Resistant Germs are extraned by the Infusion. Examples of Resistance both in Acid and Neutral Liquids " - + 194 20. Remarks on Acid, Neutral, and Alkatsaa Infusions - 203 § 21. Remarks on the Germs of Bacteria as eee from Bacteria themselves . . : - 205 § 22. Sterilization by discontinuous Heating . . 210 § 23. Mortality of Germs through defect of Oxygen produced by Exhaustion with the Sprengel Pump . : . 216 § 24. Mortality of Germs through defect of ca conse- quent on boiling the Infusion . . r + 221 § 25. Critical Review of the last two Sections . : 5 . 225 § 26. Mortality of Germs through excess of Oxygen . « » 227 § 27. Experiments on neutralized Urine . . ‘ . 228 § 28. Hermetically-sealed Flasks exposed to the Sun of the Alps . 7 3 . ‘ 5 . - » 231 § 29, Remarks on Hermetic Sealing : : : . 233 § 30. Experiments with Turnip-cheese Infusions 3 . . 234 FERMENTATION, AND ITS BEARINGS ON SURGERY AND MEDICINE . : : . . 287  Experiments on Dusty Air. Soar light, in passing through a dark room, reveals its track by illuminating the dust floating in the air. ‘The sun,’ says Daniel Culverwell, ‘discovers atomes, though they be invisible by candle-light, and makes them dance naked in his beams.’ In my researches on the decomposition of vapours by light, I was compelled to remove these ‘atomes’ and this dust. It was essential that the space con- taining the vapours should embrace no visible thing— that no substance capable of scattering light in the slightest sensible degree should, at the outset of an experiment, be found in the wide ‘ experimental tube’ in which the vapour was enclosed. For a long time I was troubled by the appearance there of floating matter, which, though invisible in diffuse daylight, was at once revealed by a powerfully condensed beam. Two U-tubes were placed in suc- cession in the path of the air, before it entered the liquid whose vapour was to be carried into the experi- mental tube. One of the U-tubes contained fragments ofmarble wetted with a strong solutionof caustic potash ; 2 THE FLOATING-MATTER OF THE AIR. the other, fragments of glass wetted with concentrated sulphuric acid which, while yielding no vapour of itsown, powerfully absorbs the aqueous vapour of the air. To my astonishment, the air of the Royal Institution, sent through these tubes at a rate sufficiently slow to dry it, and to remove its carbonic acid, carried into the experimental tube a considerable amount of mechani- cally suspended matter, which was illuminated when the beam passed through the tube. The effect was substantially the same when the air was permitted to bubble through the liquid acid, and through the solu- tion of potash. I tried to intercept this floating matter in various ways; and on October 5, 1868, prior to sending the air through the drying apparatus, it was carefully permitted to pass over the tip of a spirit-lamp flame. The floating matter then no longer appeared, having been burnt up by the flame. It was therefore organic matter. I was by no means prepared for this result; having previously thought that the dust of our air was, in great part, inorganic and non-combustible.! I had constructed a small gas-furnace, now much employed by chemists, containing a platinum tube, which could be heated to vivid redness.? Within this 1 According to an analysis kindly furnished to me by Dr. Percy, the dust collected from the walls of the British Museum contains fully 50 per cent. of inorganic matter. Ihave every confidence in the results of this distinguished chemist; they show that the jloat- ing dust of our rooms is, as it were, winnowed from the heavier matter. As bearing directly upon this point I may quote the fol- lowing passage from Pasteur: ‘Mais ici se présente une remarque: la poussiére que l’on trouve a la surface de tous les corps est soumise constamment 4 des courants d’air, qui doivent soulever-les parti- cules les plus légéres, au nombre desquelles se trouvent, sans donte, de préférence les corpuscules organisés, ceufs ou spores, moins lourds généralement que les particules minérales.’ 2 Pasteur was, I believe, the first to employ such a tube. DUST AND DISEASE. 3 tube was a roll of platinum gauze, which, while it permitted the air to pass through it, ensured the practical contact of the dust with the incandescent metal. The air of the laboratory was permitted to enter the experimental tube, sometimes through the cold, and sometimes through the heated, tube of plati- num. In the first column of the following fragment of a long table of results, the quantity of air operated on is expressed by the depression of the mercury gauge of the air-pump. In the second column the condition of the platinum tube is mentioned, and in the third the state of the air in the experimental tube. Quantity of air State of platinum tube State of experimental tube l5inches . Cold , a Full of particles. 30 yy , 7 Red-hot . 3 Optically empty. > The phrase ‘ optically empty’ shows that when the conditions of perfect combustion were present, the floating matter totally disappeared. In a cylindrical beam, which strongly illuminated the dust of the laboratory, I placed an ignited spirit- lamp. Mingling with the flame, and round its rim, were seen curious wreaths of darkness resembling an intensely black smoke. On placing the flame at some distance below the beam, the same dark masses stormed upwards. They were blacker than the blackest smoke ever seen issuing from the funnel of a steamer; and their resemblance to smoke was so perfect as to lead the most practised observer to conclude that the apparently pure flame of the alcohol lamp required but a beam of sufficient intensity to reveal its clouds of liberated carbon. But is the blackness smoke? This question pre- sented itself in a moment and was thus answered: A red-hot poker was placed underneath the beam: from 4 THE FLOATING-MATTER OF THE AIR. it the black wreaths also ascended. A large hydrogen flame was next employed, and it produced those whirl- ing masses of darkness, far more copiously than either. the spirit-flame or poker. Smoke was therefore out of the question.! What, then, was the blackness? It was simply that of stellar space; that is to say, blackness resulting from the absence from the track of the beam of al! matter competent to scatter its light. When the flame was placed below the beam the floating matter was destroyed in situ; and the air, freed from this matter, rose into the beam, jostled aside the illuminated par- ticles, and substituted for their light the darkness due to its own perfect transparency. Nothing could more forcibly illustrate the invisibility of the agent which renders all things visible. The beam crossed, unseen, the black chasm formed by the transparent air, while, at both sides of the gap, the thick-strewn particles shone out like a luminous solid under the powerful illumination. It is not, however, necessary to burn the particles to produce a stream of darkness. Without actual combustion, currents may be generated which shall displace the floating matter, and appear dark amid the surrounding brightness. I noticed this effect first. on placing a red-hot copper ball below the beam, and permitting it to remain there until its temperature had fallen below that of boiling water. The dark currents, though much enfeebled, were still produced. They may also be produced by a flask filled with hot water. 1 In none of the public rooms of the United States where I had the honour to lecture was this experiment made. The organic dust was too scanty. Certain rooms in England—the Brighton Pavilion, for example—also lack the necessary conditions. DUST AND DISEASE. 6 To study this effect a platinum wire was stretched transversely under the beam, the two ends of the wire being connected with the two poles of a voltaic battery. To regulate the strength of the current a rheostat was placed in the circuit. Beginning with a feeble current the temperature of the wire was gradually augmented ; but long before it reached the heat of ignition, a flat stream of air rose from it, which when looked at edge- ways appeared darker and sharper than one of the blackest lines of Fraunhofer in the purified spectrum. Right and left of this dark vertical band the floating matter rose upwards, bounding definitely the non- luminous stream of air. What is the explanation? Simply this: The hot wire rarefied the air in contact with it, but it did not equally lighten the floating matter. The convection current of pure air therefore passed upwards among the inert particles, dragging them after it right and left, but forming between them an impassable black partition. This elementary ex- periment enables us to render an account of the dark currents produced by bodies at a temperature below that of combustion. When the platinum wire is intensely heated, the floating matter is not only displaced, but destroyed. I stretched a wire about 4 inches long through the air of an ordinary glass shade resting on cotton-wool, which also surrounded the rim. The wire being raised to a white heat by an electric current, the air expanded, and some of it was forced through the cotton-wool. When the current was interrupted, and the air within the shade cooled, the returning air did not carry motes along with it, being filtered by the wool. At the beginning of this experiment the shade was charged with floating matter; at the end of half an hour it was optically empty. 6 THE FLOATING-MATTER OF THE AIR. On the wooden base of a cubical glass shade, a cubic foot in volume, upright supports were fixed, and from one support to the other 38 inches of platinum wire were stretched in four parallel lines. The ends of the platinum wire were soldered to two stout copper wires which passed through the base of the shade and could be connected with a battery. As in the last experiment the shade rested upon cotton-wool. A beam sent through the shade revealed the suspended matter. The platinum wire was then raised to white- ness. In five minutes there was a sensible diminution of the matter, and in ten minutes it was totally con- sumed. Oxygen, hydrogen, nitrogen, carbonic acid, so pre- pared as to exclude all floating particles, produce, when poured or blown into the beam, the darkness of stellar space. Coal-gas does the same. An ordinary glass shade, placed in the air with its mouth down- wards, permits the track of the beam to be seen crossing it. When coal-gas or hydrogen is allowed to enter the shade by a tube reaching to its top, the gas gradually fills the shade from above downwards. As soon as it occupies the space crossed by the beam, the luminous track is abolished. Lifting the shade so as to bring the common boundary of gas and air above the beam, the track flashes forth. After the shade is full, if it be inverted, the pure gas passes upwards like a black smoke among the illuminated particles. The Germ Theory of Contagious Disease. There is no respite to our contact with the floating matter of the air, We not only suffer from its mechanical irritation, but it is a growing belief that a portion of it lies at the root of a class of disorders DUST AND DISEASE, 7 most deadly toman. And what is this portion? It was some time ago the current belief that epidemic diseases generally were propagated by a kind of malaria, which consisted of organic matter in a state of motor. decay; that when such matter was taken into the body through the lungs, skin, or stomach, it had the power of spreading there the destroying process by which itself had been assailed. Such a power, it was alleged, was visibly exerted in the case of yeast. A little leaven was seen to leaven the whole lump—a mere speck of matter, in this supposed state of decomposition, being apparently competent to propagate indefinitely its own decay. Why should not a bit of rotten malaria within the human body act in a similar way? In 1836 a very unexpected reply was given to this question. In that year Cagniard de la Tour discovered the yeast- plant—a living organism, which when placed in a proper medium feeds, grows, and reproduces itself, and in this way carries on the process which we name fermentation. Here we have active life instead of motor-decay. By this discovery fermentation was con- nected with organic growth. Schwann, of Berlin, discovered the yeast-plant in- dependently about the same time; and in February, 1837, he also announced the important result, that when a decoction of meat is effectually screened from ordinary air, and supplied solely with calcined air, putrefaction never sets in. Putrefaction, therefore, he affirmed to be caused, not by the air, but by something in the air which could be destroyed by a sufficiently high temperature. The results of Schwann were confirmed by the independent experiments of Helmholtz, Ure, and Pasteur, while other methods, pursued by Schultze, and by Schroeder and Dusch, led to the same result. But as regards fermentation, the minds of chemists, 2 8 THE FLOATING-MATTER OF THE AIR. influenced probably by the great authority of Gay- Lussae, fell back upon the old notion of matter in a state of decay. It was not, they said, the living yeast-plant, but the dead or dying part of it, which, assailed by oxygen, produced the fermentation, But, as a matter of fact, when the plant is killed the ferment disappears. Mediate or immediate, the real ‘ferments’ are living organisms which find in fermentable substances their necessary food. Side by side with these researches and discoveries, and fortified by them and others, has run the germ theory of epidemic disease. The notion was expressed by Kircher, and favoured by Linnzus, that epidemic diseases may be due to germs which float in the at- mosphere, enter the body, and produce disturbance by the development within the body of parasitic life. The strength of this theory consists in the perfect parallelism of the phenomena of contagious disease with those of life. As a planted acorn gives birth to an oak, competent to produce a whole crop of acorns, each gifted with the power of reproducing its parent tree; and as thus from a single seedling a whole forest may spring ; so, it is contended, these epidemic diseases literally plant their seeds, grow, and shake abroad new germs, which, meeting in the human body their proper food and temperature, finally take possession of whole populations. There is nothing to my knowledge in pure chemistry which resembles the power of propaga- tion and self-multiplication possessed by the matter which produces epidemic disease. If you sow wheat you do not get barley; if you sow small-pox you do not get scarlet-fever, but small-pox indefinitely mul- tiplied, and nothing else. The matter of each con- tagious disease reproduces itself as rigidly as if it were (as Miss Nightingale puts it) dog or cat. DUST AND DISEASE. 9 Parasitic Diseases of Silkworms. Pasteur’s Researches. It is admitted on all hands that some diseases are the product of parasitic growth. Both in man and in lower creatures, the existence of such diseases has been demonstrated. I am enabled to lay before you an ac- count of an epidemic of this kind, thoroughly investi- gated and successfully combated by M. Pasteur. For fifteen years a plague had raged among the silkworms of France. They had sickened and died in multitudes, while those that succeeded in spinning their cocoons furnished only a fraction of the normal quantity of silk. In 1853 the silk culture of France produced a revenue of one hundred and thirty millions of franes. During the twenty previous years the revenue had doubled it- self, and no doubt was entertained as to its further augmentation. The weight of the cocoons produced in 1853 was 52,000,000 pounds; in 1865 it had fallen to 8,000,000, the fall entailing, in a single year, a loss of 100,000,000 francs. The country chiefly smitten by this calamity hap- pened to be that of the celebrated chemist Dumas, now perpetual secretary of the French Academy of Sciences. He turned to his friend, colleague, and pupil, Pasteur, and besought him, with an earnestness which the cir- cumstances rendered almost personal, to undertake the investigation of the malady. Pasteur at this time had never seen a silkworm, and he urged his inexperience in reply to his friend. But Dumas knew too well the qualities needed for such an inquiry to accept Pasteur’s reason for declining it. ‘Je mets,’ said he, ‘un prix extréme 4 voir votre attention fixée sur la question qui intéresse mon pauvre pays; la misére surpasse tout ce 10 THE FLOATING-MATTER OF THE AIR. que vous pouvez imaginer.’ Pamphlets about the plague had been showered upon the public, the mono- tony of waste paper being broken, at rare intervals, by a more or less useful publication. ‘ The Pharmacopeia of the Silkworm,’ wrote M. Cornalia in 1860, ‘is now as complicated as that of man. Gases, liquids, and solids have been laid under contribution. From eblorine to sulphurous acid, from nitric acid to rum, from sugar to sulphate of quinine,—all has been in- voked in behalf of this unhappy insect.’ The helpless cultivators, moreover, welcomed with ready trustfulness every new remedy, if only pressed upon them with sufficient hardihood. It seemed impossible to diminish their blind confidence in their blind guides. In 1863 the French Minister of Agriculture signed an agree- ment to pay 500,000 francs for the use of a remedy, which its promoter declared to be infallible. It was tried in twelve different departments of France, and found perfectly useless. In no single instance was it successful. It was under these circumstances that M. Pasteur, yielding to the entreaties of his friend, betook himself to Alais in the beginning of June, 1865. As regards silk husbandry, this was the most important department in France, and it was the most sorely smitten by the plague. The silkworm had been previously attacked by muscardine, a disease proved by Bassi to be caused by a vegetable parasite. This malady was propagated an- nually by the parasitic spores. Wafte:l by winds, they often sowed the disease in places far removed from the centre of infection. Muscardine is now said to be very rare, a deadlier malady having taken its place. This new disease is characterized by the black spots which cover the silkworms; hence the name pé. brine, first applied to the plague by M. de Quatrefages, DUST AND DISEASE. 11 and adopted by Pasteur. Pébrine declares itself in the stunted and unequal growth of the worms, in the languor of their movements, in their fastidiousness as regards food, and in their premature death. The course of discovery as regards the epidemic is this: In 1849 Guérin Méneville noticed in the blood of silkworms vibratory corpuscles, which he supposed from their motions to be endowed with independent life. Filippi, however, showed that the motion of the corpuscles was the well-known Brownian motion; but he committed the error of supposing the corpuscles to be normal to the life of the insect. Possessing the power of in- definite self-multiplication, they are really the cause of its mortality—the form and substance of its disease. This was well described by Cornalia; while Lebert and Frey subsequently found the corpuscles not only in the blood, but in all the tissues of the insect. Osimo, in 1857, discovered them in the eggs; and on this observation Vittadiani founded, in 1859, a prac- tical method of distinguishing healthy from diseased eggs. The test often proved fallacious, and it was never extensively applied. These living corpuscles first take possession of the intestinal canal, and spread thence throughout the body of the worm. They fill the silk cavities, the stricken insect often going automatically through the motions of spinning, without any material to work upon. Its organs, instead of being filled with the clear viscous liquid of the silk, are packed to distension by the corpuscles. On this feature of the plague Pasteur fixed his entire attention. The cycle of the silkworm’s life is briefly this: From the fertile egg comes the little worm, which grows, and casts its skin. This process of moulting is repeated two or three times at intervals during the life of the insect. After ' 12 THE FLOATING-MATTER OF THE AIR. the last moulting the worm climbs the brambles placed to receive it, and spins among them its cocoon. It passes thus into a chrysalis; the chrysalis becomes a moth, and the moth, when liberated, lays the eggs which form the starting-point of a new cycle. Now Pasteur proved that the plague-corpuscles might be incipient in the egg, and escape detection; they mignt also be germinal in the worm, and still baffle the microscope. But as the worm grows, the corpuscles grow also, becoming larger and more defined. In the aged chrysalis they are more pronounced than in the worm; while in the moth, if either the egg or the worm from which it comes should have been at all stricken, the corpuscles infallibly appear, offering no difficulty of detection. This was the first great point made out in 1865 by Pasteur. The Italian naturalists, as aforesaid, recommended the examination of the eggs before risking their incubation. Pasteur showed that both eggs and worms might be smitten, and still pass muster, the culture of such eggs or such worms being sure to entail disaster. He made the moth his starting- point in seeking to regenerate the race. Pasteur made his first communication on this sub- ject to the Academy of Sciences in September, 1865. It raised a cloud of criticism. Here, forsooth, was a chemist rashly quitting his proper métier and pre- suming to lay down the law for the physician and biologist on a subject which was eminently theirs. 