transparent substances like the infectious spray of droplets that 
escape from the mouths of tuberculous subjects during more or less 
violent expiratory efforts, also seems to emphasize that the tuberculous 
cow is a very important source of human tuberculosis. 
Cornet® is probably the strongest advocate of the dust-inhalation 
hypothesis. According to his views, dried, pulverized tuberculous 
sputum is the most important factor for the dissemination of tubercle 
bacilli and the transmission of tuberculosis from person to person, 
notwithstanding that he himself calls attention to the rapidity with 
which the bacilli die upon exposure to light and drying; to the 
difficulty with which a tough, sticky substance like sputum is pul- 
verized, and to the fact that only a small fraction of a mass of 
sputum can reach a sufficiently fine state of pulverization to float in 
the air, or that fine state which he believes necessary for its direct 
introduction into the finest branches of the bronchial tubes. 
Sunlight is the most potent, natural agent for the sterilization of 
tubercle bacilli; it kills them in less than one hour when they are 
exposed to its direct rays in translucent layers of infectious pus, and 
in less than five hours when they are exposed in thick, opaque masses 
of such pus . * * 6 TTeinzirl c asserts that tubercle bacilli, as well as other 
nonsporulating pathogenic bacteria, are destroyed in from two to ten 
minutes by direct sunlight, and Koch, d Jousett, e Fliigge/ Heymann ,* 7 
Di Donna , 6 Cadeac,* and others earlier called attention to the rapidity 
with which tubercle bacilli are destroyed by desiccation and exposure 
to light. 
If light and drying are the potent factors for the destruction of 
tubercle bacilli the practical evidence shows them to be, it becomes 
questionable whether tuberculous sputum, which is so tough that it is 
difficult to pulverize in a mortar with a pestle after it has been 
thoroughly dried, ever reaches a state of pulverization in nature that 
will enable it to float in the air without first wholly losing its infec- 
tiousness. Of course, there are scores of ways in which moist tuber- 
culous sputum is dangerous, and hence the rapidity with which light 
destroys tubercle bacilli and the difficulty with which sputum is 
pulverized must not be taken as facts that justify or excuse careless 
spitting. 
* 
°Die Tuberkulose, Vienna, 1907. pp. 101-117. 
6 Bureau of Animal Industry Circular No. 127, pp. 17-20. 
c Dept. Agr. Expt. Sta. Bee., Vol. XIX, Xo. 3, p. 280, 1907. (Jour. Infect. 
Diseases. May, sup. 3, pp. 128-153.) 
d Comet, Die Tuberkulose, p. 41. Vienna, 1907. 
e Wiener Med. Wocbens, 1901, No. 28, p. 1366. 
f Zeitscbrift fur Hygiene, vol. 38. 
^ Editorial Jour. Arner. Med. Asso., Oct. 12, 1901. 
6 Centralb. fur Bact. und Parisitenk, Vol. XLII, No. 7. 
* Le Bulletin Medical, Sept. 5, 1906, 
