166 MICRO-ORGANISMS AND DISEASE. [CHAP. 



tuberculous tissue. These pure bacilli, no matter how many 

 times they have been transferred, no matter how far removed 

 from their original breeding-ground, always produced the 

 characteristic disease when inoculated into suitable animals. 

 The cultivation succeeded equally with material derived from 

 human tubercles, from bovine tubercles, and from the artifici- 

 ally-induced tuberculosis of guinea-pigs. The bacilli grow 

 well at a temperature varying between 37 and 39 C. in 

 solid serum, Agar-Agar peptone mixture, and solidified 

 hydrocele fluid. 1 (See Chapter II.) An incision is made 

 into a tubercle with clean (overheated) scissors and a particle 

 of a tubercle is taken up with the point of a clean (overheated) 

 needle and deposited on the top of one of these sterile solid 

 media kept in a test-tube plugged with sterile cotton-wool. 

 After keeping it for ten days to a fortnight in the incubator at 

 37 to 39 C. the first traces of growth make their appearance 

 in the shape of small dry whitish scales, which gradually 

 increase in size until they coalesce. These scales are made 

 up of the typical tubercle-bacilli lying closely side by side ; 

 some of the bacilli are longer, others shorter, and many of 

 them have spores. New cultures may be established 

 from these bacilli. Inoculation with them or with further 

 cultivations into the subcutaneous tissue, peritoneal or pleural 

 cavity of guinea-pigs and rabbits, produces after three, four, 

 or more weeks, the typical lesions characteristic of artificial 

 tuberculosis ; namely, swollen lymphatic glands near the 

 seat of inoculation, with subsequent caseation and ulceration ; 

 enlargement of the spleen due to numerous whitish tubercles, 

 the larger ones caseous ; enlargement of the liver, which is 

 mottled by the presence of uniformly distributed whitish 



1 Solidified hydrocele fluid has been successfully used for the cultiva- 

 tion of the tubercle-bacilli, not by Koch, but by my friend Mr. Makins 

 of St. Thomas's Hospital. 



