SECRETORY FUNCTIONS IN HUMAN PLACENTA 525 



That the corpus luteum is a kind of internally secreting organ 

 (from the histological point of view) was advocated by Prenan- 

 as early as 1898 and by Born in 1900. Subsequently, the argu- 

 ment has been advanced with more certainty by a close 

 histological study conducted by Regaud and Policard ('01), 

 Fr. Cohn ('03), Mulon ('09), Athias ('11), Van der Stricht ('12), 

 Tsukaguchi ('12, '13), and Levi ('13). And the main ground 

 of this argument lies in nothing but that the luteal cells con- 

 tain as formative ingredients of the cell bodies plastosomes and 

 lipoid granules, and often demonstrate a very large quantity 

 of vacuoles which may be deemed their secreted matter, and 

 also that the close correlation between these ingredients func- 

 tionally is plainly apparent in the same manner as it is seen in 

 external secretory cells. Of the various ingredients mentioned 

 above, lipoid granules certainly have the most important signifi- 

 cance in internal secretion; however, since the latter is not 

 only characteristic of luteal cells, but is also widespread among 

 the other kinds of internal secreting cells, Tsukaguchi has 

 already argued that it would be proper, in view of its functions, 

 rather to compare them with the secreting granules of ordinary 

 glandular cells. 



In the next place, Cohn first regarded the vacuoles in a rab- 

 bit as a secreted matter of the luteal cell, and he saw them simply 

 as a dissolved product of lipoids ; subsequently Tsukaguchi also 

 studied the same animal, and likewise deemed them a modified 

 product of hpoids. However, vacuoles differ exceedingly in the 

 degree of their development in all kinds of animals. For in- 

 stance. Van der Stricht did not notice any vacuoles in the 

 luteal cell of a bat, and subsequently Levi's observations 

 regarding the same animal nearly agreed with those of Van der 

 Stricht. In the guinea-pig, however, Levi noticed a small num- 

 ber of vacuoles, which he attributed to a retrogressive phenom- 

 enon of the cell concerned, and he stated that this phenom- 

 enon, by means of a chemical change of lipoids following 

 it, could cause possibly the substance of the latter to be 

 dissolved by the benzol and xylol which had been used by 

 him as clearing media. In short, whenever the vacuoles 



