THE BIOLOGY OF MICROBES, ETC. 145 



Bacterium photometricum. According to Dr. 

 T. W. Engelmann, 1 this microbe is influenced by 

 light ; in fact, its movements are stated to depend 

 on light. It produces a red pigment, but the 

 amount of pigment formed varies with the action of 

 light. Different coloured lights affect this bacterium 

 differently, the most powerful being the ultra-red, 

 the yellow, and part of the green. 



Bacterium crassum sputigenum. This microbe was 

 originally isolated from sputum ; it also occurs in 

 the 'fur' scraped from the tongue. It measures 1 /* 

 in length and 0*8 /A in breadth. Colonies on gelatine 

 plates appear as grey, viscid drops, and in needle 

 cultures develop a nail-shaped growth. This mic- 

 robe is fatal to mice, rabbits, and dogs. 



Bacterium pneumonicum agile. This is the mic- 

 robe of vagus pneumonia of rabbits. The cells are 

 short thick rods, which occur singly or in chains of 

 three or four. This bacterium forms dark granular 

 colonies on gelatine, which subsequently liquefies. 

 It also grows on blood serum, bouillon, and potatoes. 

 The growth on potatoes spreads very rapidly over 

 the whole surface as a red layer. Pure cultures of 

 this microbe are fatal to rabbits. 



Bacterium violaceum. This microbe was dis- 

 covered by Bergonzini, 2 and it measures from 2 to 3 

 p in length, and from 0'6 to 1 p, in breadth. It 

 occurs on egg-albumin, forming a violet pigment. 

 This pigment is insoluble in water, and soluble "in 



1 PJluger's Archiv, vol. xxx. p. 95; Revue Internal. Science, 

 tome ix. (1882), p. 469. 



2 Ann. Soc. Nat. Moden., vol. xiv. 



K 



