DEVELOPMENT OF THE BACTERIA. 113 



Cohn, in order to better observe the phenomena 

 and to get rid of the moulds, which the cane-sugar 

 caused to develop too rapidly, employed the fol- 

 lowing culture-fluid : 



Distilled water .... 100. 

 Tar tr ate of ammonia . . 1. 

 Ashes of yeast .... 1. 



Bacteria develop in this fluid wonderfully, which 

 proves that sugar is not indispensable to them. 



One other solution often employed is that of 

 Mayer. It has the advantage of not requiring the 

 employment of ashes of yeast : 



Phosphate of potash . . .0.1 gramme. 

 Sulphate of magnesia . . . 0.1 

 Tribasic phosphate of lime . 0.1 

 Distilled water 20 c.c. 



Cohn adds to this 0.2 gr. tartrate of ammonia. 



En resume, the bacteria can take nitrogen, which 

 they need in order to form their protoplasm, either 

 from albuminous compounds, which they decom- 

 pose, as in putrefaction, or in the form of am- 

 monia, or, perhaps, by borrowing it from nitric 

 acid, but this last source is not well established 

 (Cohn). 



Carbon. In addition to the sources common 

 to other organisms, the bacteria can take this im- 

 portant element of their composition, under cer- 

 tain circumstances, from the organic acids. Thus, 

 when we cultivate bacteria in a solution containing 



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