122 MICRO-ORGANISMS AND DISEASE. [CHAP. 



the peripheral portion of the cell. But according to Koch the 

 bacilli by and by disappear again from the giant-cells. 



The bacilli do not show any motility and often include 

 spores ; they are thus capable of forming spores within the 

 body. Owing to these spores, human phthisical sputum re- 

 tains its virulence even after drying for considerable periods. 

 Koch cultivated the bacilli artificially, i.e. outside the body, 

 and by carrying on the cultivation for several successive trans- 

 missions succeeded in isolating and clearing them from the 

 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 cha- 

 racteristic 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 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 lym- 

 phatic glands near the seat of inoculation, with subsequent 

 caseation and ulceration ; enlargement of the spleen due to 

 numerous whitish tubercles, the larger ones caseous ; enlarge- 

 ment of the liver, which is mottled by the presence of uni- 

 formly distrilated whitish points and streaks, which by and by 

 become confluent and caseous ; tuberculosis of the peritoneum ; 

 isolated tubercles in the lungs, at first grey and transparent, 



1 Solidified hydrocele fluid has been successfully used for the cultivation of 

 the tubercle-bacilli, not by Koch, but by my friend Mr Makins of St. Thomas's 

 Hospital. 



