308 PATHOGENIC BACTERIA. 



duced to grow upon a mixture of commercial ammonium 

 carbonate, o. 35 per cent. ; primary potassium phosphate, 

 0.15 per cent; magnesium sulphate, 0.25 per cent.; 

 glycerin, 1.5 percent. It was even found that tuberculin 

 was produced in this inorganic mixture. 



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. 



It 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 thickness of the mass 

 exposed to its influence. 



At one time the widespread character of tuberculosis 

 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 1 has shown that this is untrue, and that tubercle 

 bacilli exist only in the atmospheres contaminated 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 pul- 

 verized 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 



1 Zeilschrifi fiir Hygiene, v. 



