76 



THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM, 



Fig. 3. — Spermatogonium, spermatocyte, and spermatid 

 of mouse, showing (a) similar diffuse arrangement of 

 mitochondria, (b) secondary circumnuclear condensation, 

 (c) final even distribution in the cytoplasm. (After 

 N. H. Cowdry, 1917.) 



from it. In the later stages of spermatogenesis they leave the nucleus, becoming 

 more resistant to acetic acid, as Regaud (1910, p. 298) has shown. Indeed, the 

 parallelism is very close (figs. 2 and 3). The Lewises (1915, p. 349) have observed 

 mitochondria journeying to the nucleus and back again in the living cells of tissue 

 cultures. Here their movements are much more rapid and no change in com- 

 position is evident. What their mission is we have no idea. 



They also gather together in the peripheral cytoplasm, just beneath the cell- 

 membrane, especially in animal cells. This arrangement is very pronounced in 

 egg-cells and it has often been alluded to by Van der Stricht (1909, plate 1) and 

 his pupils. It is a general phenomenon for 

 which there must be some explanation. 

 After a time the mitochondria become 

 redistributed, just as in the perinuclear 

 condensations. Curiously enough, other 

 cells, like gland-cells, rarely if ever show 

 it. An interesting reversal of this condi- 

 tion is seen in certain pathological con- 

 ditions where the mitochondria quit the 

 peripheral cytoplasm and become heaped 

 up about the nucleus instead. 



Both perinuclear condensations and peripheral condensations frequently occur 

 in one and the same cell, as in the ascidian eggs described by Loyez (1909, p. 192). 



In ciliated epithelial cells the mitochondria are often permanently heaped up 

 in the region of the cytoplasm just beneath the ciliated border. I have found that 

 this is the case in the ciUated cells of the epididymis of the white mouse. This 

 fact, together with the familiar clumping of mitochondria about the axial filament 

 in the tail of the spermatozoon and the feeling that they are transformed into 

 myofibrils, led Benda to the conclusion that they play a part in the motor activities 

 of the cell. 



The clumpi7ig and fusion of mitochondria to form other substances is to be 

 regarded as a very special instance of modifications in their arrangement. A dis- 

 cussion of this process logically falls under the heading of histogenesis. It may be 

 simply mentioned here that we come across it in the formation of the nebenkern, 

 the spiral filament, certain portions of the rods and cones of the retina, and other 



structures. 



It is unnecessary to go into a discussion of other minor variations in the 

 arrangement of mitochondria, dependent upon the deposition of substances in the 

 cytoplasm, upon j^ressure, and other obvious causes. 



In all these journey ings of mitochondria to and fro, and in these transitory and 

 permanent condensations and fusions, not a shred of evidence can be seen that they 

 possess powers of independent motility like bacteria. The prevalent belief that 

 they do possess these powers seems to be simply a relic of the old conception of 

 Altmann that they are elementary organisms endowed with all vital properties, 

 just as the idea that in all cases they arise from other mitochondria by longitudinal 

 or transverse division persists under the guise of the misleading doctrine of mito- 



