THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 141 



XII. DISCUSSION. 

 THE GENERAL RESULTS OF MITOCHONDRIAL WORK. 



(1) It constitutes a definite addition to our knowledge of the fundamental 

 structure of Living material, for we have found in them a definite and concrete 

 class of cell granulation presenting even less variation than the chromatins and 

 distributed through almost all Uving matter. 



(2) The discovery of their fatty, phosphatid nature (just when physiological 

 chemists are becoming interested in fats, whereas formerly their chief attention 

 was devoted to the study of proteins, owing to the inspiration of Emil Fischer's 

 work on protein synthesis), is a coincidence of some importance because it makes 

 probable a rapprochement between cytological and chemical work, a new and 

 promising point of contact having been established. 



(3) The fact that they do serve, in some cases, as a basis for cell classification 

 may prove to be of great value when followed up. This is particularly true in ques- 

 tions of cell genealogy. The differences, however, in the appearance of mitochon- 

 dria in cells of different type are usually but sUght, and this is not to be wondered 

 at in view of the generality of their distribution in all protoplasm and in view also of 

 the probabihty that they play their part in some fundamental activity common to 

 many cells, not in highly speciaUzed functions Ukely to differ from cell to cell. 



(4) In embryology they have excited the greatest interest. The radical claims 

 concerning their role in histogenesis have forced the reinvestigation of the entire 

 field. There is much difference of opinion, but it can be safely said that they are 

 associated in the formation of certain substances like fat, Upoid, pigment, and per- 

 haps also secretion granulations. While it seems clear that they do not form these 

 substances by direct chemical transformation, the exact part which they play is 

 a mystery and will probably remain so for some time to come. In inheritance also 

 much has been done, but no good experimental evidence has been found in support 

 of the supposition that they act as carriers of heredity. 



(5) With regard to the part which they play in the physiology of the cell, we 

 have learned only that it is fundamental rather than specialized. We suspect 

 that they are concerned either directly or indirectly with processes of metabolism 

 or protoplasmic respiration, and this is as far as we can go. 



(6) The extraordinary sensitivity of mitochondria to pathological change 

 has already proved of the greatest value in experimental medicine. It has been 

 found that, in some cases, they are much more sensitive than the nucleus. Prepa- 

 rations made by the old methods designed to give nuclear detail show no trace 

 whatever of the more subtle changes which may be brought to light by the newer 

 mitochondrial technique. Furthermore, since the mitochondria are so different from 

 the nucleus in every respect, it is not surprising that they have proved themselves 

 to be indicators of an entirely different type of activity. It is in fact this quality 

 which has been of such great service in the study of exophthalmic goiter (p. 136). 



(7) In botany the study of mitochondria has greatly advanced our knowledge 

 of the development of plastids. It has been found that the plastids arise from the 



