2i6 PRACTICAL BACTERIOLOGY. 



that are still warm, and the tuberculous organs taken 

 out with sterilised knives. These organs are then 

 cut up with instruments which are frequently being 

 changed and freshly sterilised, so that freshly cut 

 small portions maj be continually taken up. One of 

 these pieces is then crushed between two scalpels, or 

 better, it is placed upon a freshly sterilised sheet of 

 zinc, and broken up with the scalpel. A small quan- 

 tity of this material is then taken up with a sterilised 

 platinum wire, and spread over the blood serum, care 

 being taken to disturb the surface as little as possible. 

 The test-tubes which have been inoculated in this way 

 are then made air-tight in the manner described be- 

 fore, by means of india-rubber caps, and are kept at a 

 temperature of 37° to 37'5° C. in the incubator. The 

 temperature must be kept as constant as possible. 



After a lapse of fourteen days, the first naked eye 

 indications of the formation of colonies can be per- 

 ceived in those tubes which have remaiued unconta- 

 minated with other bacteria, and which contain 

 tubercle bacilli. Little whitish specks appear, which 

 in time become converted into dry scales, and which 

 rest loosely on the nutrient medium. These scales 

 never run together, but may be lifted up one by one 

 from the blood serum ; they are very characteristic in 

 their general appearance of tubercle bacilli, for no 

 other kind of bacterium grows in a similar manner 

 upon blood serum. If some blood serum which has 



