THE MITOCHONDRIAL CONSTITUENTS OF PROTOPLASM. 119 



the following theory of secretion: The mitochondrial filaments fix the substances 

 which the cell takes up from the blood. At one or more points in the course of 

 each filament there is an accumulation and elaboration of these materials, and at 

 these points the filament swells up into spherules to which one can apply the name 

 of "plastes." Each plast gives rise to a grain which matures and grows little by 

 little. Usually before the grain has acquired its definitive size and colorability the 

 mitochondrial filament in which it is embedded becomes paler and can no longer 

 be seen. The plast or grain is then set free in the protoplasm. At the moment 

 of excretion there is a dissolution and the product passes in the dissolved state 

 through the cell-wall. By this ingenious and plausible hypothesis they overcome 

 the difficulty of assuming that the mitochondria form the secretion through actual 

 chemical transformation. 



F.4.T DROPLETS IN SEBACEOUS GLANDS. 



Nicolas, Regaud and Favre (1912a, p. 203), working on human tissues, have 

 done little beyond confirming Altmann's observation of vesicular mitochondria 

 in the cells of sebaceous glands. Arguing from analogous appearances in other 

 tissues, they suggest that these give rise to the droplets of fat, but they do not 

 attempt to describe any transitions between the two and advance no evidence in 

 support of their suggestion. 



SECRETION OF S^^■EAT GLANDS. 



Here also Nicolas, Regaud and Favre (19126, p. 191) have studied the rela- 

 tions of mitochondria to secretion. They have found a relationship between the 

 number of mitochondria and the number of secretion granules, but they have failed 

 to discover any indication of the granules developing within the mitochondria as 

 in the parotid and submaxillary glands. They emphasize the fact that in sweat 

 glands the mitochondria are small and usually granular, and they say that even if 

 the granules did arise within them, as they believe to be the case, it would be diffi- 

 cult to observe it. 



SECRETION OF MAMMARY GLANDS. 



Hoven (1911, p. 325) has made a careful study of mitochondria in resting 

 and lactating mammary glands. He has arri\'ed at the conclusion that they play 

 a part in the formation of the different constituents of the milk. According to 

 him, the mitochondria break up into granulations, some of which transform into 

 grains of secretion, which give rise to the casein and the sugar; others transform 

 into fat. 



SECRETION OF THE PROSTATE. 



Akatsu (1903, p. 566) gave the first clear-cut description of mitochondria, 

 under the heading of "Altmann's granules," in the cells of the prostate. He ex- 

 pressed the opinion that they gave rise to granules of secretion. More recently 

 Dominici (1913. p. 295) has worked over the entire question and has found that 

 the mitochondria vary cjuantitatively with the activity of the cell. He thinks, 

 however, that they play an indirect part in the formation of the secretion and that 

 they are not directly transformed into it. He claims that De Bonis (1907, p. 14) 



