vi TUBERCLE BACILLI IN MILK 107 



Examine next day. 



Pick out the smallest colonies which appear suspi- 

 cious, and make subcultures on sloped agar-agar, 

 and keep the latter at 38'5 C. At the same 

 time make a microscopic examination of the 

 suspicious colonies (vide p. 78). 



Streptococci and diphtheria bacilli, if present in 

 sufficient number, can readily be detected in this 

 manner. 



If diphtheria bacilli be suspected, instead of agar-agar, 

 sloped serum agar-agar may be used with great advantage 

 (vide p. 92). 



(c) Sample E : Tubercle bacillus (Van Ketel's method). 



(1) To 200 cc. of the suspected milk add 10 cc. of strong 

 liquefied carbolic acid or 10 grammes of carbolic acid 

 crystals. 



(2) Shake vigorously in a well-corked flask for two to 

 five minutes. 



(3) Now pour the carbolised milk into a conical urine 

 glass, and allow it to stand under a glass cover for twenty- 

 four hours. 



(4) With a fine capillary pipette remove a little from 

 the deepest layer of the sediment, and prepare films in 

 the usual manner, by rubbing it between two cover-glasses. 



(5) Allow the films to dry in the air and pass them 

 three times through the flame. 



(6) Now pass the films through a solution of alcohol 

 and ether (equal parts). 



