432 E. V. COWDRY 



RELATION TO METABOLISM 



There is amp'e evidence that mitochondria play an active 

 and fundamental role in cell activity, though just what the part 

 is, is obscure. 



The first fact of interest is their wide occurrence. They occur 

 in the majority of the cells of all animals which have been in- 

 vestigated, with adequate methods of technique, from man to 

 the most lowly protozoan. Plants also contain them. They 

 are most abundant in the active stages of the life of the cell. 

 They diminish progressively in number as the cells become 

 senile. The most striking example of this is seen in sections of 

 the skin as one passes from the cells of the deeper layers, which 

 contain many mitochondria, to the more superficial, desquamat- 

 ing cells, which are dead or dying and which often are quite 

 devoid of mitochondria. Moreover, the mitochondria decrease 

 in number as one passes from nucleated to nonnucleated red 

 blood cells. Indeed, Shipley ('15, p. 83) has shown that the 

 persistence of a few mitochondria in nonnucleated red blood 

 cells is indicative of the fact that they are young and vigorous. 

 It is well known that mitochondria are particularly abundant 

 in immature, embryonic cells, which as yet exhibit no specialized 

 activity, but in which metabolic processes are very active. 



Direct experimental evidence is also at hand. There are 

 many observations on quantitative variations in mitochondria 

 with cell activity. Thus Romeis ('13, p. 12) has found that 

 mitochondria are very numerous in actively regenerating tis- 

 sues; Busacca ('15, p. 232) found that they decreased in number 

 with fatigue in the cells of the retina stimulated with intense 

 light; Homans ('15, p. 12) associated the number of the mito- 

 chondrial filaments with an increased activity of islet cells in 

 experimental diabetes; Policard ('10, p. 284) showed that there 

 was an increase in the number of mitochondria in kidne}^ cells 

 on administration of phloridzin, and so on. 



These statements relate, however, only to the general impression 

 given by the study of sections. There has been no attempt to 

 distinguish, in a clear cut way, between absolute and relative 



