2r8 PRACTICAL BACTERIOLOGY. 



They must, however, of course be kept at a tem- 

 perature above 29° C, as below this their growth 

 is entirely arrested ; at blood heat it is only mode- 

 rately rapid. Variations of temperature of even only 

 tenths of degrees may exert an influence upon the 

 rapidity of their growth. This bacillus does not 

 thrive in gelatine, on account of the above-mentioned 

 peculiarities; it develops in bouillon at blood heat, 

 but its growth is not characteristic. 

 W-' Exceedingly similar to this bacillus, both in its mor- 

 phological characters and in its behaviour towards 

 staining reagents, is the bacillus of fowls'tuberculosis. 

 The form of the colonies, however, is somewhat 

 different ; and also in its pathogenic peculiarities 

 towards certain animals it shows a not inconsiderable 

 variation. For instance, the bacillus of fowls' tuber- 

 culosis does not form small dry scales on blood serum, 

 but a more even, mucoid, whitish coating; moreover, 

 these bacilli, as a rule, are not pathogenic in guinea- 

 pigs, which are so exceedingly susceptible to tuber- 

 culosis. 



Bacilli were first discovered in leprous patients a 

 long time ago, being collected together in great 

 masses in the tissue cells of the leprosy nodules. 

 These bacilli are exceedingly similar to those of tuber- 

 culosis, only they are generally somewhat shorter and 

 thicker. In their behaviour towards staining re- 

 agents they also resemble tubercle bacilli, except that 



