THE TESTICLE AND THE OVARY 361 



Those cases already referred to, in which atrophy of the uterus 

 took place after the removal of the ovaries, also indicate the 

 dependence of the menstrual and prooestrous functions upon the 

 presence of ovarian tissue, since normal heat could not occur if 

 the uterus were in a condition of fibrotic degeneration, while certain 

 of Knauer's experiments 1 afford evidence that heat can be experi- 

 enced by animals in which the ovaries are transplanted to abnormal 

 positions. 



Veterinarians are generally agreed that heat does not occur in 

 dogs whose ovaries have been extirpated. Moreover, ovariotomy is 

 sometimes practised on mares in order to prevent OBstrus, and so 

 suppress the vicious symptoms which are liable to render the animals 

 periodically unworkable. 2 



The spaying of sows is a well-known commercial practice, and if 

 properly carried out prevents the recurrence- of "heat." The ordinary 

 method is to make an incision in the side and withdraw the u,terus 

 along with the ovaries, but sometimes one or both ovaries are left 

 behind, and the sows come " in use." This has led to the discrediting 

 of the practice, the importance of removing the minute ovaries 

 (the pigs being only about seven weeks old) not being properly 

 appreciated. 8 



Dr. Jolly and the author* have shown, further, that normal 

 prooestrum, followed by oastrus, can occur in dogs which only possess 

 transplanted ovaries, thus confirming the observations of Knauer and 

 Halban. In the experiments in question the animals' own ovaries 

 were removed, and a few weeks later the ovaries obtained from 

 other dogs were grafted in abnormal positions (e.g. between the 

 abdominal muscular layers or on the ventral border of the peritoneal 

 cavity). The grafts seem to have become attached, and to have 

 survived for a sufficiently long period to exercise an influence over 

 the generative system ; but they eventually underwent consider- 

 able fibrous degeneration, as the post-mortem evidence afterwards 

 showed. 



As a result of these experiments it may probably be concluded 

 that the enhanced activity which the ovaries exhibit during the 

 final stages of follicular development is accompanied by metalwlic 

 changes which result in an increase in the production of the ovarian 

 secretion, and that this phenomenon is the main factor in the periodic 



1 Knauer, !<><: ,-it. 



2 Hobday, "Ovariotomy of Troublesome Mares," Veterinary Jour., New 

 Series, vol. xiii., April 1906. 



3 Mackenzie and Marshall, "Ovariotomy in Sows, etc.," Jour, of Agrir. 

 Science, vol. v., 1913. See below, p. 389. 



4 Marshall and Jolly, "Contributions to the Physiology of Mammalian 

 Reproduction : Part II. The Ovary as an Organ of Internal Secretion," /'/>//. 

 Trans., B., vol. cxcviii., 1905. 



12 A 



