THE GENERAL CONDITIONS OP LIFE 



287 



these plants are the exact reverse of animals : they take up 

 carbonic acid and give off oxygen. So long as the sunlight acts 

 upon their green leaves, they need no oxygen. A green plant, 

 therefore, can be kept alive in a space free from oxygen, if it be 

 allowed to stand in the light and receive carbonic acid. But this 

 taking-in of carbonic acid and giving-out of oxygen is not the 

 plant's respiration. In reality, as 

 has already been seen,^ the plant 

 like the animal inspires oxygen and 

 expires carbonic acid. This fact is 

 simply disguised by the process of 

 assimilation. During the night, how- 

 ever, when assimilation ceases in the 

 darkness, the plant inspires oxygen 

 and expires carbonic acid ; and, if it 

 be cultivated in a closed space, it 

 lives during the night upon the 

 oxygen that it has set free during 

 the day by the cleavage of the car- 

 bonic acid that it has taken in. The 



process of assimilation of carbonic 



acid is, therefore, to be sharply 



separated from that of respiration. 



The two phenomena are entirely 



distinct from one another. 



But in a peculiar kind of organ- 

 isms, the so-called AnaeroMa, the 



relations are even much less clear 



than in the plants. The AnaeroMa 



are organisms, belonging chiefly to 



the Bacteria, that can continue to 



live with complete absence of oxygen. 



Many of them even perish when they 



come in contact with free oxygen. 



Since Pasteur, the father of Bac- 

 teriology, first asserted the reality 



of such rare beings, their actual 



existence has frequently been 



doubted, but there is no longer any 



question of the correctness of this 



claim. Thus, e.g., the bacteria of symptomatic anthrax and of 



tetanus grow anaerobically (Fig. 131). So, also, the vibrios of 



cholera are able to live admirably in alkaline nutrient media with 



absence of air ; under these conditions they increase rapidly in the 



intestine, where scarcely a trace of pure oxygen exists. This fact 



is the more remarkable since when brought into contact with air 



1 Cf. p. 173. 



IG. 131. — A. Culture of ihe bacteria of 

 symptomatic anthrax. (After Migula.) 

 The spherical colonies lie in the interior 

 of nutrient gelatine excluded from the 

 air. B, Culture of the bacteria of 

 tetanus. The bacteria have liqueiied 

 the lower part of the nutrient gelatine 

 in the test-tube and have formed a 

 bubble of gas, which lies at the upper 

 end of the liquefied mass. They have 

 gi-own only in the lower parts of the 

 test-tube, separated from the air by a 

 thick layer of gelatine. 



