The strength of expiration from the lungs also contributes to loudness. Manipulation of the larynx is used to generate a source sound with a particular fundamental frequency, or pitch. This source sound is altered as it travels through the vocal tract, configured differently based on the position of the tongue, lips, mouth, and pharynx. The process of altering a source sound as it passes through the filter of the vocal tract creates the many different vowel and consonant sounds of the worlds languages as well as tone, certain realizations of stress and other types of linguistic prosody. The larynx also has a similar function to the lungs in creating pressure differences required for sound production; a constricted larynx can be raised or lowered affecting the volume of the oral cavity as necessary in glottalic consonants. The vocal cords can be held close together (by adducting the arytenoid cartilages) so that they vibrate (see phonation). The muscles attached to the arytenoid cartilages control the degree of opening. Vocal cord length and tension can be controlled by rocking the thyroid cartilage forward and backward on the cricoid cartilage (either directly by contracting the cricothyroids or indirectly by changing the vertical position of the larynx), by manipulating the tension of the muscles within the vocal cords, and by moving the arytenoids forward or backward. This causes the pitch produced during phonation to rise or fall. In most males the vocal cords are longer and have a greater mass than most females vocal cords, producing a lower pitch.
As the campaign neared its goal, Fenner and his team played an important role in verifying eradication. The last naturally occurring case of indigenous smallpox (Variola minor) was diagnosed in Ali Maow Maalin, a hospital cook in Merca, Somalia, on 26 October 1977. The last naturally occurring case of the more deadly Variola major had been detected in October 1975 in a three-year-old Bangladeshi girl, Rahima Banu.The global eradication of smallpox was certified, based on intense verification activities, by a commission of eminent scientists on 9 December 1979 and subsequently endorsed by the World Health Assembly on 8 May 1980. The first two sentences of the resolution read:

Having considered the development and results of the global program on smallpox eradication initiated by WHO in 1958 and intensified since 1967 … Declares solemnly that the world and its peoples have won freedom from smallpox, which was a most devastating disease sweeping in epidemic form through many countries since earliest time, leaving death, blindness and disfigurement in its wake and which only a decade ago was rampant in Africa, Asia and South America. Costs and benefits
The cost of the eradication effort, from 1967 to 1979, was roughly US$300 million. Roughly a third came from the developed world, which had largely eradicated smallpox decades earlier. The United States, the largest contributor to the program, has reportedly recouped that investment every 26 days since in money not spent on vaccinations and the costs of incidence.