348 Tuberculosis 



days of pathology clearly saw that the time must come 

 when the parasitic nature of tuberculosis would be proved, 

 and Klebs, Villemin, and Cohnheim were "within an ace" 

 of its discovery, and Baumgarten* probably saw it in tissues 

 cleared with lye, it remained for Robert Koch to demon- 

 strate and isolate the Bacillus tuberculosis, the specific 

 cause of the disease, and to write so accurate a description 

 of the organism and the lesions it produces as to be almost 

 without a parallel in medical literature. 



Distribution. So far as is known, the tubercle bacillus is 

 a purely parasitic organism. It has never been found 

 except in the bodies and discharges of animals affected with 

 tuberculosis, and in dusts of which these are component 

 parts. This purely parasitic nature interferes with the 

 isolation of the organism, which cannot be grown upon 

 the ordinary culture media. 



The widespread distribution of tuberculosis at one time 

 suggested 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 t has, however, shown this to be untrue, 

 as tubercle bacilli exist only in atmospheres contaminated 

 by consumptives. His experiments were made by collecting 

 dusts from streets, sidewalks, houses, rooms, walls, etc., and 

 injecting them into guinea-pigs, whose constant suscepti- 

 bility to the disease makes them very appropriate for 

 its detection. In this way Cornet showed the bacilli to 

 be present only in dusts with which pulverized sputum was 

 mixed, and found such infectious dusts to be most common 

 where the greatest uncleanliness prevailed. 



Our present knowledge of the life-history of the tubercle 

 bacillus, by showing its disposition to multiply outside the 

 bodies of animals, the deleterious influence of sunlight 

 upon it, the absence of positive permanent forms, and its 

 sensitivity to temperatures beyond certain extremes, con- 

 firms all that Cornet has pointed out, and also explains 

 why, in the course of time, the expectoration of con 

 sumptives has not rendered the atmosphere pestilential. 



Morphology. The tubercle bacillus is a slender, rod- 

 I shaped organism with slightly rounded ends and a slight 

 curve. It measures from 1.5-3.5 /* in length and from 



* "Virchow's Archives," Bd. LXXXII, p. 397. 



t "Zeitschrift fur Hygiene," v, 1888, pp. 191-331. 



