CHAP, i.] FEMALE ORGANS. 1501 



are brought about. It is no more difficult to suppose that the 

 stimulus of the enlargement of a Graaffian follicle causes nutritive 

 as well as vascular changes in the uterine mucous membrane, than 

 it is to suppose that the stimulus of food in the alimentary canal 

 causes those nutritive changes in the salivary glands or pancreas 

 which constitute secretion. In the latter case we can to some 

 extent trace out the chain of events ; in the former case we 

 hardly know more than that the maintenance of the lumbar cord 

 is sufficient, as far as the central nervous system is concerned, for 

 the carrying on of the work. In the case of a dog in which the 

 spinal cord had been completely divided in the thoracic region 

 while the animal was as yet a mere puppy, ' heat ' took place as 

 usual. And, though ' heat ' is something different from human 

 menstruation the two are probably, in this respect, analogous. 



