338 THE PHYSIOLOGY OF REPRODUCTION 



the corpus luteum might be to provide an internal secretion 

 which assisted in the attachment of the embryo to the uterine 

 mucosa. Unable to undertake the investigation himself, he 

 persuaded Ludwig Fraenkel to put his theory to an experi- 

 mental test. For this purpose a series of experiments upon 

 rabbits was proceeded with, the ovaries being removed at 

 intervals varying from one to six days after the occurrence 

 of coition, the period of gestation in this animal being thirty 

 days. The rabbits were afterwards killed, when it was found 

 that the extirpation of the ovaries had prevented the fixation of 

 the embryos, or had caused these to be aborted. In other cases 

 the corpora lutea are described as having been burnt out by 

 the electric cautery without destroying the rest of the ovaries, 

 and these experiments led to a similar result. Control experi- 

 ments were performed by removing one ovary while leaving 

 the other, and by destroying some of the corpora lutea but not 

 all, and in the majority of these cases the animals produced 

 young. The experiments resulted, therefore, in supporting the 

 view that there is an intimate connection between the presence 

 of the corpus luteum and the occurrence of pregnancy, and that 

 this connection is in a certain sense one of cause and effect. 



Apart from the experimental evidence, Fraenkel adduces 

 certain other facts which tend to support the theory that the 

 corpus luteum is an organ of internal secretion. He points 

 out that its general structure is eminently suggestive of its 

 being a ductless gland, since it is formed mainly of large 

 epitheloid cells surrounded by a network of capillaries and 

 arranged in regular rows or columns not unlike those of the 

 cortex of the supra-renal body. Moreover, the increase in the 

 size of the corpus luteum, until it becomes larger than a Graafian 

 follicle, seems inexplicable on any other view. This unusual 

 capacity for growth is clearly out of all proportion to that of 

 the rest of the ovary, and it is pointed out, further, that when 

 the corpus luteum is most hypersemic, the other part of the 

 ovary is unusually anaemic, while towards the end of pregnancy, 

 when the increase in the blood supply to the generative organs 



1 Fraenkel and Cohn, " Experimentelle Untersuchungen iiber den Einfluss 

 des Corpus Luteum auf die Insertion des Eies," Anat. Anz., vol. xx., 1901 ; 

 Fraenkel. loc. cit. 



