TUBERCULOSIS. 221 



The tubercle bacillus seems to require a considerable 

 amount of oxygen for its development. It is also pecu- 

 liarly sensitive to temperatures, not growing at a tem- 

 perature below 29 C. or above 42 C. Temperatures 

 above 75 C. kill it after a short exposure. 



The tubercle bacillus does not develop well in the 

 light, and when its virulence is to be maintained should 

 always be kept in the dark. Sunlight kills it in from 

 a few minutes to several hours, according to the thick- 

 ness of the mass exposed to its influence. 



The widespread character of tuberculosis at one time 

 suggested the idea that tubercle bacilli were ubiquitous 

 in the atmosphere, that we all inhaled them, and that it 

 was only our vital resistance that prevented us all from 

 becoming its victims. 



Cornet must be given the credit of having shown that 

 such an idea is untrue, and that tubercle bacilli only 

 exist in the atmospheres frequented by consumptives. 

 His experiments were made by collecting dusts from 

 numerous places streets, sidewalks, houses, rooms, walls, 

 etc. Injecting them into guinea-pigs, whose constant 

 susceptibility to the disease makes them a very delicate 

 reagent for its detection, Cornet showed the bacilli to be 

 present only in the dust with which pulverized sputum 

 was mixed, and found such infectious dust to be most 

 common where the greatest carelessness in respect to 

 cleanliness prevailed. 



Our present knowledge of the life-history of the tubercle 

 bacillus, by showing its indisposition to multiply outside 

 the bodies of animals, the deleterious influence of sun- 

 light upon it, the absence of positive permanent forms, 

 and its sensitivity to temperatures beyond a certain range, 

 confirms all that Cornet has pointed out, and shows us 

 why the expectoration of millions of consumptives has 

 not rendered our atmospheres pestilential. 



As long as tuberculosis exists among men or cattle, it 

 shows that the existing hygienic precautions are insuf- 



