114 PHYSIOLOGY OF THE BACTERIA. 



only tartrate of ammonia with a small quantity of 

 mineral salts (phosphoric acid, potash, sulphuric 

 acid, lime, and magnesia), they develop rapidly, 

 taking their carbon from the tartaric acid. 



Cohn has endeavored to ascertain if other or- 

 ganic acids could be assimilated by the bacteria. 

 By making use of succinate of ammonia, or neutral 

 acetate of ammonia, he has been able to cultivate 

 these microphytes. Besides, as Pasteur had already 

 experimented with solutions containing lactates, and 

 in which bacteria had developed until the salt had 

 completely disappeared, we may admit that the 

 bacteria can assimilate the organic acids, — tartaric, 

 succinic, acetic, and lactic ; but tartaric acid seems 

 to furnish the best alimentary solution. 



Other substances containing carbon are also as- 

 similated by the bacteria, — cane-sugar, milk-sugar, 

 glycerjne, and even cellulose (according to Mit- 

 scherlich). 



Cohn concludes, " that the bacteria multiply quite 

 normally, and in great quantity, whenever they 

 find the elements in solution which constitute 

 ashes, and that they can take the carbon which 

 they need from any organic substance containing 

 it, and their nitrogen from ammonia, urea, and 

 probably from nitric acid. The bacteria, then, re- 

 semble green plants, in that they assimilate nitro- 

 gen contained in their cells by taking it from 

 ammonia compounds, which animals cannot do. 

 They differ from green plants in that they cannot 

 draw their carbon from carbonic acid, and only 

 assimilate organic substances containing carbon, 



