BACILLUS OF TUBERCULOSIS. 267 



The tubercle bacillus when exposed to direct sunlight 

 is killed in from a few minutes to several hours, accord- 

 ing to the thickness of the layer and the season of the 

 year; it is also usually destroyed by diffuse daylight in 

 from five to seven days when placed near a window. 

 This fact is worthy of note, as it has an important 

 hygienic bearing. Thus, tuberculous sputum expector- 

 ated upon sidewalks, etc., being exposed to the action 

 of direct sunlight, will in many cases, especially in 

 summer, be disinfected by the time it is in a condi- 

 tion to be carried into the air as dust. For the same 

 reason, consumptive patients should occupy light, sunny 

 rooms and live as much as possible in the open air and 

 exposed to the action of direct sunlight. 



The tubercle bacillus is a strict parasite that is to 

 say, its biological characters are such that it could 

 scarcely find natural conditions outside of the bodies 

 of living animals favorable for its multiplication. But 

 it has been noted that when it is cultivated for a time 

 in artificial media containing glycerin it may grow on 

 the surface of plain veal or chicken bouillon, in which 

 media it fails to develop when introduced directly from 

 a culture originating from the body of an infected ani- 

 mal. This would indicate the possibility of its acquir- 

 ing the ability to grow as a saprophyte. The experi- 

 ments of Nutall also show that the bacillus may multi- 

 ply, under favorable conditions, in tuberculous sputum 

 outside of the body. Notwithstanding these facts, 

 it is probable that the growth of tubercle bacillus out- 

 side of the living bodies of man and animals is so 

 slight as to have no practical importance in causing 

 infection. 



On account of their slow growth and the special con- 



