402 INTERNAL SECRETION 



These authors assume that the mammalia are divisible into two 

 groups, those in which ovulation is spontaneous, and those in 

 which it is provoked by sexual advances. The first group in- 

 cludes man, the dog, horse, pig, cow and certain other species; 

 females of this class possess, in addition to the corpus luteum 

 graviditatis, a second corpus luteum, which develops periodically, 

 is homologous to the interstitial gland, and fulfils the function 

 of the latter. The second group, which is represented by the 

 rabbit, guinea-pig, mouse and cat, is furnished with an enor- 

 mously developed interstitial tissue and with a corpus luteum 

 graviditatis, but possesses no periodic corpus luteum. 



It is evident from the facts which have been advanced, that 

 there is no justification, either for such a classification of mam- 

 mals, or for any homology of the corpus luteum menstruationis 

 with the interstitial tissue. The corpus luteum is a homogeneous 

 structure, which proceeds from the epithelial portion of the 

 Graafian vesicle ; while the interstitial gland is another and dif- 

 ferent ovarian tissue element derived from the atretic follicles and 

 of connective-tissue origin, the elements of which have a structural 

 resemblance to true lutein cells and possess, moreover, a secretory 

 function. 



In what does the function of these two tissues consist? It 

 is not possible, at present, to arrive at a satisfactory answer to 

 this question. We shall have occasion later to describe the 

 hypotheses which have been advanced concerning the functions of 

 the corpus luteum. In so far as the interstitial ovarian gland 

 is concerned, it is probable that this tissue, like Leydig's cells in 

 the testis, is the site at which the specific hormone is produced, 

 by which the correlative activity of the entire ovary is effected. 

 The material at our disposal is, however, insufficient to support 

 such a hypothesis, and the results of investigation are, moreover, 

 largely contradictory. 



The interstitial gland attains very marked development, not 

 only before puberty and menstruation that is to say, at the period 

 of increased ovarian function but also during pregnancy (under 

 physiological and, to an even greater extent, under pathological 

 conditions) when, for many reasons, we are led to assume a 

 reduction of internal secretory function on the part of the ovaries. 

 It is during pregnancy that extensive cystic degeneration of the 

 follicles and formation of theca-lutein cells takes place (O. Fell- 

 ner, Cohn). On the other hand, Wallart recently observed cases 

 of osteomalacia unaccompanied by pregnancy, in which there was 

 marked development of the interstitial gland. 



If the functional activity of the interstitial gland is estimated 

 in accordance with the degree of its anatomical development, it 

 appears probable that this tissue is active at puberty, during 

 menstruation, and in pregnancy ; up to the present, however, no 

 evidence is forthcoming to show the manner in which this internal 

 secretory activity affects the organism. 



