132 THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



angiosperms to the fungi, though their existence is doubtful in the myxomycetes, 

 schizomycetes, and most of the algse. They are apparently identical in both plants 

 and animals (N. H. Cowdry, 1917, p. 225). They are indeed as characteristic 

 of the cytoplasm as chromatin is of the nucleus. They differ .slightly in composi- 

 tion just as chromatin does. The fact that they are most abundant in the active 

 stages of life of the cell and decrease in number as the cell becomes old and senile 

 is not without significance. We find them in the egg and in all the tissues of the 

 developing embryo — from the very beginning (when the cells have no definite 

 specialized activities) to the later stages and adult life, when each has assumed 

 its own pecuhar duty of secreting or contracting, or conducting, as the case may 

 be. In other words, their presence in the absence of speciaUzed activities indicates 

 that, in these early days of development, they are either inert or else play a part 

 in the fundamental vital processes. The conclusion is obvious; and since they do 

 not differ in any noteworthy particular in the later stages, the assumption is justi- 

 fied that here also their function is a basic generalized one. 



The meager and unsatisfactory yet direct experimental evidence at hand 

 seems to support this view. Thus Romeis (1913c, p. 12) has found that mitochon- 

 dria are very numerous in actively regenerating tissues; Busacca (1915, p. 232) 

 found that they decreased in number with fatigue in the cells of the retina stimu- 

 lated with intense light; Homans (1915, p. 12) associated the number of mitochon- 

 drial filaments with an increased activity of islet-cells in experimental diabetes; 

 Policard (1910, ]). 284) showed that there was an increase in the number of 

 \ mitochondria in kidney-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 fluctuations in mitochondrial content. The 

 observations have not been controlled by a careful estimation of cell-volumes. 

 Thurlow (1917, p. 37) has been the first to realize these discrepancies. She has 

 established a definite mitochondria cytoplasmic rate in the nerve-cell, just as 

 Hertwig years ago measured the nucleus c}'topla.smic ratio (see p. 80). 



There have been no carefully checked observations on qualitative changes 

 in mitochondria with cell activity, although we have abundant evidence that the 

 solubilities of mitochondria vary. Of course, the changes in form of mitochondria 

 have been subjected to careful scrutiny, but so far they have yielded httle of value. 

 The observations of Holmgren (1909, p. 308) on the changes in mitochondria in 

 muscular fatigue are quahtative in a sense and very interesting, but they have 

 never been confirmed. 



Furthermore, processes of metabohsm, as well as of respiration, are, as one 

 would naturally expect, very easily modified in pathological states; hence the 

 sensitivity of mitochondria to pathological change. Scott (1916, p. 243) discov- 

 ered that the mitochondria are the first of all the cell constituents of the pancreas 

 to become altered in experimental phosphorus poisoning. Moreover, the fact 

 (which is now emerging from the numerous recent pathological studies on mito- 

 chondria) that mitochondria in different types of cells respond in much the same 



