30 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



difference in the reactions of bacteria and mitochondria to 

 temperature. 



Chemical constitution. The chemical nature of mito- 

 chondria has been presumed to be a phosphatid combined 

 with albumin. The reasons for this assumption were dis- 

 cussed in the previous chapter. Wliile the evidence, so far 

 as it goes, points to the presence of phosphatids in the 

 mitochondria of the liver cells, it is probable that they are 

 also present in other mitochondria. There is no evidence, 

 however, to indicate that the phosphatid-albumin complex 

 is the only constituent of mitochondria. 



Certainly the chemical determinations that have been 

 made on mitochondria and bacteria are not sufficient to 

 justify the conclusion that the two groups of structures are 

 fundamentally different in chemical constitution. So far 

 as the reactions of mitochondria to physical, chemical, and 

 thermal agents have been the basis for determining their 

 nature, the responses of bacteria to these same agents 

 would rather suggest a similarity of the two groups of 

 structures. 



In a series of studies on ferment action, JobUn and Peter- 

 sen ('14a, b, c) have determined the presence of lipoids in 

 bacteria. It may not be amiss to quote their opinion in 

 this connection. ''Bacteria do, however, contain fats and 

 lipoids in varying amounts, which because of their marked 

 effect on surface tension, would for purely physical reasons 

 tend to become concentrated at the periphery of a colloidal 

 system such as the bacterial protoplasm. With or without 

 a morphologically distinct limiting membrane we can reason- 

 ably assume that the external surface of the bacterial cell 

 is potentially lipoidal." 



The results of these experiments and the analysis of 

 mitochondrial Uterature failed to reveal any evidence that 

 excluded the possibihty that mitochondria may be bacterial 

 in nature. On the other hand, many properties that have 



