THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 



81 



show no evidence of fatty substances on histological examination may neverthe- 

 less actually contain a large amount as revealed by chemical analysis, and vice 

 versa. The mitochondria are phosphatids, not neutral fat. It may also be urged 

 that the cell contains a large variety of phosphatids of different solubilities and 

 that our mitochondrial methods bring to light only those of a certain kind. This 

 is undoubtedly true, but it is not the whole story, because our technique reveals 

 all the phosphatids which occur in definite form and may be seen in the living cell, 

 so that we are studying a constant, not a variable thing. 



A word of caution in connection with the interpretation which we may justly 

 place upon variations in the amount of mitochondria: In many pathological 

 conditions there is a deposition of lipoids within the cell, the so-called lecithin 

 metamorphosis. These must be carefully distinguished from true mitochondria. In 

 other cases deposits of neutral fat occur which may be detected by the fact that 

 they reduce osmic acid. Moreover, these substances almost invariably occur as 

 spherules, very rarely as filaments, as is usually but not always the case with the 

 mitochondria. 



The total absence of mitochondria in normal actively functioning cells which 

 are not senile (p. 79) is of considerable interest, though it is in all probability 

 a phenomenon of very rare occurrence. Most of the examples recorded have, 

 on further examination, proved to be erroneous; for instance, the parietal cells of 

 the stomach, myeloblasts, the cells of malignant tumors, and others. I have never 

 succeeded in finding mitochondria in tissue mast-cells, but I am inchned to think 

 that this may simply be due to the acidophilic mitochondria being obscured by the 

 densely packed basophilic granulations. They are present, however, in blood 

 mast-cells. The cells in the kidney of 

 snakes, described by Regaud (1908a, p. 17), 

 and the cells of the glomeruU of embry- 

 onic human kidneys (PoUcard, 19120, p. 

 442; 12/, p. 12) have never been found to 

 contain mitochondria. Branca (1911, p. 

 559) has failed to find them in the in- 

 ferior or germinative zone of hairs. Other 

 cases of the apparent absence of mito- 

 chondria may be cited. 



In neighboring cells of the same type, 

 which usually contain approximately the 

 same amount of mitochondria, we occasionally come across variations in amount 

 from cell to cell which are difficult to explain. One cell sometimes contains mito- 

 chondria in tremendous excess of the normal amount present in the cells on either 

 side of it. The dilTerence may be so striking as to lead us to think at first sight 

 that we are dealing with a different kind of cell altogether. In others there may be 

 a decrease. The decrease is,. I believe, often indicative of bad technique, just as 

 we have learned to attribute to the same cause the artificial polymorphism of 

 mitochondria in cells where they are normally alike. The increase I am unable 



Figs. 7, 8, and 9. — Neural tube, myotome, and Wolffian 

 duct, showing cells apparently normal yet devoid of 

 mitochondria. 



