20 SYMBIONTICISM AND THE ORIGIN OF SPECIES 



connection, it is also of importance as an indication of a possible 

 relationship between the amount of mitochondria and the phois- 

 phatid lecithin. 



The "evidence" here deals with possibilities and not with 

 pertinent facts. 



In summing up, we find that only one piece of investiga- 

 tion, that of Mayer, Rathery and SchaefTer has definite 

 bearing on the problem. It relates only to the mitochondria 

 of the cell of a single organ, — the liver. While we can 

 neither deny, nor affirm the phospholipin-albumin constitu- 

 tion of mitochondria, there is no reason to conclude that 

 mitochondria have the same constitution in all kinds of 

 cells, and at all periods in the life of the cell. We certainly 

 are not justified in rejecting the work that has been done on 

 the histogenesis of fibrils on the basis of an incompatibility 

 with the assumed chemical constitution of mitochondria. 

 We must frankly confess that the chemical constitution of 

 mitochondria is not known. It is interesting to note that 

 Cowdry himself recognizes the variabihty of the chemical 

 constitution of mitochondria, in other parts of his thesis 

 (p. 85). He suggests that this variabihty may be more 

 apparent than real: "it may be due to factors other than a 

 difference in the mitochondria — to changes in the water 

 content, for example." This, it appears to me, is a weak 

 substitute for the rational interpretation suggested by such 

 variations. 



Mathews ('15), in his text book on Physiological Chem- 

 istry, states that the phospholipins or phosphatids are 

 "among the most important substances in living matter. 

 For they are found in all cells, and it is undoubtedly their 

 function to produce with cholesterol, the pecuHar semifluid, 

 semisohd state of protoplasm. The latter holds much water 

 in it, and does not dissolve. Indeed it might be said that the 

 phosphatids with cholesterol make the essential physical 

 substratum of hving matter." Let us then assume that the 



