BACILLUS TUBERCULOSIS. 267 



to form a thin, dull covering over the surface of the 

 serum. On further inoculation of these cultivations on 

 new blood serum the growth takes place more readily ; 

 later cultivations give more luxuriant growths, which 

 also spread over the surface of the drop of fluid present 

 at the lower part of the tube. When 

 examined under a low power of the 

 microscope (80 diameters) the appear- 

 ance of the colonies is seen to be 

 very peculiar and characteristic. After 

 five to six days very peculiar and 

 delicate figures are seen on the 

 surface of the blood serum, forming 

 finely curved and S-shaped lines ; Fig 78 .Lcolonies of 

 these gradually spread and form tubercle bacilli from 



J . a cultivation, dried 



masses which ultimately become and stained on a 

 united with one another. These 

 colonies can be obtained by pressing a cover glass on 

 the surface of the serum, and they can then be stained 

 and the individual bacilli recognised under high powers 

 of the microscope. 



Koch has made in all 43 cultivations from tubercular 

 material ; several of these being from bovine tuberculosis, 

 scrofulous glands, fungous disease of joints, and lupus. 

 Some of these cultivations have been now kept up 

 through more than forty generations for over three 

 years ; but the bacilli have in no way lost their viru- 

 lence. Another soil on which they can grow is a mix- 

 ture of infusion of meat with agar, but the growth on 

 this material is by no means so good. Koch was only 

 able to obtain a cultivation in neutralised meat infusion 

 under special conditions, and in -this material the 

 bacteria formed, after four or five weeks, a white, 

 granular deposit at the bottom of the clear fluid. No 

 growth could be obtained on any vegetable substance. 

 The development of the bacilli completely ceases below 

 28 or 29 C. ; at 30 C. it is very slow; it is best 

 between 37 and 38, and completely ceases at 42. 

 The difficulty of cultivation and the narrow limits with- Cultivation 

 in which growth occurs has been confirmed by other h/fanS?* 8 



observers. 



