BIOLOGICAL PROPERTIES 417 



for 24 hours at 37 C. the medium is slightly cloudy, and on the surface a 

 viscous pellicle is formed which makes a ring round the tube just above the 

 surface of the liquid. On further incubation the pellicle 

 falls to the bottom of the tube leaving the broth cloudy 

 and viscous. 



Gelatin. Stab culture. Incubated at 20 C., a small 

 raised white growth is formed on the surface of the gelatin 

 after 48 hours : the growth later extends along the line 

 of the stab and assumes a typical nail-line appearance. 

 The medium is not liquefied. Bubbles of gas often form 

 around the growth. 



Isolated colonies. Small round granular whitish colonies, 

 which become somewhat raised, appear towards the third 

 day. 



Agar. Coagulated serum. Growth on these media takes 

 the form of a thick white viscous layer. 



Potato. A thick yellowish and viscous streak is formed 

 and gas is also produced. 



Milk. The medium is coagulated sometimes rapidly 

 and at other times more slowly. In the first sub-culture 

 some strains of the bacillus do not coagulate milk but 

 on further sub-cultivation they quickly acquire this property 

 (Denys and Martin). 



SECTION III. BIOLOGICAL PROPERTIES. FIG. 224. Pneumo- 



bacillus. Stab culture 



1. Vitality and virulence. Cultures of the pneumo- in gelatin. Tthday. 

 bacillus are rapidly killed at 60-80 C., but in dry 



albuminous matter the bacillus is much more resistant : it seems to retain 

 both its virulence and its vitality for a long time in water and soil. The 

 virulence of different strains of the pneumobacillus is subject to con- 

 siderable variations ; it is possible that there are different varieties of the 

 organism (the Bacillus lactis aerogenes would be one of these varieties, see 

 p. 415). 



2. Toxin. Filtered cultures contain a toxin which is fatal to rabbits and 

 produces symptoms of paralysis. Post mortem the intestines are congested 

 and show small haemorrhages . 



3. Bio-chemical reactions. Indol. Nitrites. In a neutral 3 per cent, 

 solution of peptone the pneumobacillus does not produce indol. It forms 

 nitrites out of nitrates. 



Fermentation reactions. The pneumobacillus ferments glycerin, and 

 certain of the carbohydrates, viz. : glucose, galactose, arabinose, mannite, 

 dulcite, saccharose^ lactose, maltose, ramnose and dextrin, but is without 

 action on erythrite. Frankland has described a strain which does not 

 ferment glycerin. 



Grimbert recommends the following medium for the study of the fermentation 

 reactions : 



Test substance, 3 grams. 



Dry peptone, ... 2 



Water, - - 100 c.c 



Calcium carbonate, - Quantum sufficit. 



The formation of gas is naked-eye evidence of fermentation. If the calcium 

 carbonate be omitted and litmus solution added the blue colour of the latter is 

 changed to red during the fermentation. Glycerin is more slowly broken up. 



2D 



