History
In the early 1920s, an outbreak occurred of a previously unrecognized cattle disease in the northern United States and Canada. Cattle were haemorrhaging after minor procedures, and on some occasions spontaneously. For example, 21 of 22 cows died after dehorning, and 12 of 25 bulls died after castration. All of these animals had bled to death.In 1921, Frank Schofield, a Canadian veterinary pathologist, determined that the cattle were ingesting moldy silage made from sweet clover, and that this was functioning as a potent anticoagulant. Only spoiled hay made from sweet clover (grown in northern states of the US and in Canada since the turn of the century) produced the disease. Schofield separated good clover stalks and damaged clover stalks from the same hay mow, and fed each to a different rabbit. The rabbit that had ingested the good stalks remained well, but the rabbit that had ingested the damaged stalks died from a haemorrhagic illness. A duplicate experiment with a different sample of clover hay produced the same result. In 1929, North Dakota veterinarian Lee M. Roderick demonstrated that the condition was due to a lack of functioning prothrombin.The identity of the anticoagulant substance in spoiled sweet clover remained a mystery until 1940. In 1933, Karl Paul Link and his laboratory of chemists working at the University of Wisconsin set out to isolate and characterize the haemorrhagic agent from the spoiled hay. Five years were needed before Links student, Harold A. Campbell, recovered 6 mg of crystalline anticoagulant.
Eyes are organs of the visual system. They provide living organisms with vision, the ability to receive and process visual detail, as well as enabling several photo response functions that are independent of vision. Eyes detect light and convert it into electro-chemical impulses in neurons (neurones). In higher organisms, the eye is a complex optical system which collects light from the surrounding environment, regulates its intensity through a diaphragm, focuses it through an adjustable assembly of lenses to form an image, converts this image into a set of electrical signals, and transmits these signals to the brain through complex neural pathways that connect the eye via the optic nerve to the visual cortex and other areas of the brain. Eyes with resolving power have come in ten fundamentally different forms, and 96% of animal species possess a complex optical system. Image-resolving eyes are present in molluscs, chordates and arthropods.The most simple eyes, pit eyes, are eye-spots which may be set into a pit to reduce the angle of light that enters and affects the eye-spot, to allow the organism to deduce the angle of incoming light. From more complex eyes, retinal photosensitive ganglion cells send signals along the retinohypothalamic tract to the suprachiasmatic nuclei to effect circadian adjustment and to the pretectal area to control the pupillary light reflex. Overview
Complex eyes distinguish shapes and colours. The visual fields of many organisms, especially predators, involve large areas of binocular vision for depth perception.