Isolation and Cultivation 321 



being maintained for four or five hours each day. The 

 medium appears yellowish and is usually dry, so that before 

 using it is well to use a few drops of water to make conditions 

 appropriate for the growth of the tubercle bacillus. 



N on- albuminous Media. It is really surprising to note 

 the extremely simple compounds upon which the tubercle 

 bacillus can be accustomed to grow. Instead of requiring 

 the most concentrated albuminous media, as was once 

 supposed, Proskauer and Beck * have shown that the 

 organism can be made to grow in non-albuminous media 

 containing asparagin, and that it can even be induced 

 to grow upon a mixture of commercial ammonium car- 

 bonate, 0.35 per cent.; primary potassium phosphate, 0.15 

 per cent.; magnesium sulphate, 0.25 per cent.; glycerin, 1.5 

 per cent. Tuberculin was produced in this mixture. 



a b 



Fig. 96. Bacillus tuberculosis: a, Source, human; b, source, bovine. 

 Mature colonies on glycerin-agar. Actual size (Swithinbank and 

 Newman). 



Appearance of the Cultures. Irrespective of the media 

 upon which they are grown, cultures of the tubercle bacil- 

 lus present certain characteristics which serve to separate 

 them from the majority of other organisms, though insuffi- 

 cient to enable one to certainly recognize them. 



The bacterial masses make their appearance very slowly. 

 As a rule very little growth can be observed at the end of a 

 week, and sometimes a month must elapse before the 

 cultures can be described as well grown. 



They usually develop more rapidly upon fluid than upon 

 solid media. The growth is invariably and purely aerobic, 



* " Zeitschrift fur Hygiene," Aug. 10, 1894, xvm, No. 1. 



21 



