Isolation and Cultivation 363 



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 will grow. Instead of requiring the most concen- 

 trated 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 carbonate, 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. 



Fig. no. 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. 



