114 DISTRIBUTION OF MITOCHONDRIA IN THE PLACENTA. 



because an important role is ascribed to these structures. The uterine glands of 

 the pig's placenta are credited, according to several investigators (Ercolani, 1869; 

 Bonnet, 1882) with liberating a profuse secretion, termed the uterine milk, which 

 finds its way onto the surface of the uterine mucosa, where it is absorbed by the cho- 

 rionic epithelium and thus constitutes one of the main sources of fetal nutriment. 



Mitochondria are equally numerous in the placenta of the cat. They occur 

 chiefly in the broad layer of chorionic epithelium which intervenes between the 

 circulation of the mother and that of the offspring. They are also abundant in 

 the delicate layer of endothelium which incloses the maternal blood-channels. 

 Little has been reported concerning the histochemistry of the cat's placenta 

 beyond the fact that the chorionic epithelium contains numerous fat droplets 

 (Melissenos, 1906). Recently, one of the authors (Wislocki, 1920) has studied the 

 behavior of the cat's placenta toward trypan blue injected into the maternal blood- 

 stream. It was found that trypan blue does not pass from mother to fetus but is 

 stored in the form of minute granules in the cytoplasm of the chorionic epithelium 

 and the endothelial cells which line the maternal blood-vessels. These are the cells 

 whose cytoplasm, as described, is filled with mitochondria. 



In the guinea-pig mitochondria are found in great profusion in the syncytium 

 which comprises the bulk of the placental labyrinth and separates the maternal from 

 the fetal blood-stream. Fat and glycogen are also readily demonstrable in the 

 syncytium and trypan blue is deposited there when injected into the maternal cir- 

 culation. The placenta of the guinea-pig possesses numerous degenerating cells of 

 both fetal and maternal origin and it is interesting to note that these cells lose their 

 mitochondria while undergoing degeneration. 



In the human placenta, also, it is the syncytium and Langhans cells which con- 

 tain mitochondria in greatest abundance. It need only be emphasized that these are 

 the cells which separate the two circulations and in which products of metabolism, 

 such as glycogen (Driessen, 1907) and fat (Hofbauer, 1910) are amply demonstrable. 



In conclusion it is interesting to consider what significance can be ascribed to 

 the mitochondria in the placenta. It is striking that they are most numerous in 

 those cells of the placenta which are presumed to play an important role in the 

 metabolic transfer between the two organisms. From observations such as we have 

 made, however, it is impossible to assign to them any specific function. The only 

 conclusion one can safely draw concerning mitochondria is that they represent 

 material which is probably used in the multiphasic activities of the placental cells. 



