34 LEO LOEB. 



position suitable for copulation. 1 This sign is, however, of no 

 use when the animals are timid or when a number of the females 

 are kept in the pen ; under those conditions they pile up in a corner 

 when one tries to touch them. 



'The condition of the vulva may be of value in determining 

 the state of the female. If a drop of mucus can be seen in the 

 vulva, the animal is not in heat, even if acting somewhat ex- 

 citedly, but it will be found in heat within a few hours. At the 

 times of heat we find usually a little moisture or almost dried 

 mucus at the vulva and a slight enlargment or swelling of the 

 entrance to the vagina which may be so slight that it becomes 

 noticeable only if the animal is compared with others. 



" In some, perhaps in most cases, a day or two before heat the 

 animal while not showing any of the above-mentioned signs, 

 may be unusually lively and playful, and when taken in hand and 

 brushed very lightly over pelvic region, we notice a twitching 

 about the pelvis and especially the vulva." 



VII. EFFECT OF EXTIRPATION OF THE OVARIES ON THE CYCLIC 



CHANGES IN THE UTERUS. 



We found that extirpation of the corpora lutea shortens the 

 sexual cycle. It does not to any noticeable extent influence the 

 various stages in the development of the ovarian follicles, but it 

 causes an early rupture of mature follicles. Extirpation of the 

 corpora lutea changes however the cyclic changes in the uterus. 

 It prevents the predecidual proliferation of the connective tissue 

 cells of the mucosa and modifies also to some extent the cyclic 

 changes in the uterine epithelium. It does not however prevent 

 those changes in the uterus which accompany heat and precede 

 ovulation. The existence of a corpus luteum is required only as 

 far as a certain part of the cyclic changes in the uterus is con- 

 cerned; certain other changes (those preceding ovulation) are 

 in all probability in a similar manner as ovulation itself inhibited 

 by the existence of a functionating corpus luteum. However, 

 if we extirpate both ovaries instead of the corpora lutea, all 

 cyclic changes in the uterus come to a standstill. 



1 A similar observation had been previously communicated to me by Mr. J. M. 

 Simpson. 



