BACILLI IN CHRONIC INFECTIOUS DISEASES. 385 



but Roux and Nocard say that the most favorable temperature ap- 

 pears to be 39, and that development is slower at 37. 



The experiments of Koch, Schill and Fischer, and others show 

 that the bacilli retain their vitality in desiccated sputum for several 

 months (nine to ten months De Toma) ; but they are said to undergo 

 a gradual diminution in pathogenic virulence, which is more rapid 

 when the desiccated material is kept at a temperature of 30 to 40 C. 

 In the experiments of Cadeac and Malet portions of the lung from 

 a tuberculous cow, dried and pulverized, produced tuberculosis in 

 guinea-pigs at the end of one hundred and two days. They retain 

 their vitality for a considerable time in putrefying material (forty- 

 three days Schill and Fischer ; one hundred and twenty days Ca- 

 deac and Malet). The resisting power of this bacillus against ger- 

 micidal agents is also greater than that of certain other pathogenic 

 microorganisms, but not so great as to justify the inference that it 

 forms spores. It is not destroyed by the gastric juice in the sto- 

 mach, as is shown by successful infection experiments in suscep- 

 tible animals, 'by mixing cultures of the bacillus with their food 

 (Baumgarten, Fischer), and also by experiments with an artificially 

 prepared gastric juice (Falk). They are destroyed, in sputum, in 

 twenty hours by a three-per-cent solution of carbolic acid, even 

 when they present the appearance usually ascribed to the presence 

 of spores (Cavagnis) ; also by absolute alcohol, a saturated aqueous 

 solution of salicylic acid, saturated aniline water, etc. (Schill and 

 Fischer). The more recent experiments of Yersin upon pure cul- 

 tures of the bacillus gave the following results : " Tubercle bacilli, 

 containing spores, were killed 1)y a five-per-cent solution of carbolic 

 acid in thirty seconds, by one-per-cent in one minute ; absolute alco- 

 hol, five minutes ; iodof orm-ether, one per cent, five minutes ; ether, 

 ten minutes ; mercuric chloride, 1 : 1,000 solution, ten minutes ; 

 thymol, three hours ; salicylic acid, 2. 5 per cent, six hours. 



The tubercle bacillus appears to be especially susceptible to the 

 action of light. In his address before the Tenth International Medi- 

 cal Congress (Berlin, 1890) Koch says that when exposed to direct 

 sunlight the tubercle bacillus is killed in from a few minutes to sev- 

 eral hours, according to the thickness of the layer ; it is also de- 

 stroyed by diffuse daylight in from five to seven days when placed 

 near a window. This fact has an important hygienic bearing, espe- 

 cially in view of the fact that the tubercle bacillus is not readily 

 killed by desiccation, putrefaction of the material containing it, etc. 

 Tuberculous sputum expectorated upon sidewalks, etc., being ex- 

 posed to the action of direct sunlight, will in many cases be disin- 

 fected by this agent by the time complete desiccation has occurred 

 i. e. , before it is in a condition to be carried into the air as dust. 

 30 



