33° • PATHOGENIC BACTERIA. 



While occasional desultory experiments have been 

 made, and from time to time investigators have per- 

 formed inoculation experiments, the subject seems to have 

 met its most thorough study at the hands of Smith. 1 He 

 carefully compared a series of bacilli obtained from human 

 sputum with a series obtained from the tuberculous lesions 

 of cattle, horses, hogs, cats, dogs, and other animals. 



Briefly summarized, his observations lead us to the 

 following conclusions : 



1. Vegetation. — The human tubercle bacillus grows 

 upon dog's serum much more luxuriantly and rapidly than 

 the bovine bacillus. 



2. Morphology. — The size of the bovine forms is very 

 constant, the individuals being quite short (1-2 //). They 

 are straight, not very regular in outline, and sometimes 

 of a spindle, sometimes a barrel, and sometimes an oval 

 shape. The bacilli of human tuberculosis, on the other 

 hand, are prone to take an elongate form under artificial 

 cultivation. 



3. Staining. — The bacillus of bovine tuberculosis 

 usually takes an even color with readiness ; that of hu- 

 man tuberculosis differs in presenting more irregularity 

 of penetration, by which the so-called beaded appearance 

 is produced. They are also more apt to contain rounded, 

 deeply-staining bodies suggestive of spores, at or near the 

 ends. When grown upon very moist surfaces many of 

 the bacilli of human tuberculosis are stained with great 

 difficulty. 



4. Pathogenesis. — a. Guinea-pigs. — The bacilli of bovine 

 tuberculosis are much more virulent than those of human 

 tuberculosis, intraperitoneal inoculation of the former 

 producing death in adult animals in from seven to sixteen 

 days; of the latter, in from ten to thirty-eight days. Sub- 

 cutaneous inoculation of the bovine bacillus causes death 

 in less than fifty days; of the human bacillus, in from 

 fifty to one hundred days. 



1 Transactions of the Association of American Physicians, 1896, xi., p. 75. 

 "and 1898, xiii., p. 417. 



