CHANGES IN THE MATERNAL ORGANISM 491 



sympathetic system has an effect only in so far as it modifies 

 the circulatory conditions. The only change observed, after 

 destruction of the lumbar cord, was a prolongation of the act 

 of parturition, due to an absence of pain and the consequent 

 loss of the reflex contractions of the abdominal muscles. The 

 most important nervous elements for the uterus are contained 

 in the uterine, paracervical, and paravaginal ganglia, but their 

 excitability for external stimuli gradually decreases during 

 pregnancy and is lost at the end. 



We are thus forced to conclude that the phenomena of 

 pregnancy and parturition are brought about by chemical 

 stimuli acting through the blood-stream. The hormone or 

 hormones may arise in the corpus luteum, which is essential for 

 the progress of pregnancy, at least in the early stages (Marshall 

 and Jolly *). Evidence is also forthcoming that the mammary 

 secretion is due to an ovarian influence in certain cases. For 

 instance, secretion may occur in virgin women who are the 

 subjects of ovarian tumours, and in virgin bitches. Cramer 2 has 

 recorded a case in which the transplantation of ovaries into a 

 woman, whose genital organs were much atrophied, led to a secre- 

 tion of colostrum. 3 On the other hand, removal of the ovaries 

 at the middle of pregnancy does not interfere with the second 

 half of the period of gestation, or with labour and lactation. 1 



The presence of the placenta may modify the normal meta- 

 bolism in various ways. It is set in the path traversed by the 

 formative material on its way to the embryo, and by the waste 

 products excreted by the embryo. The form in which the 

 materials required by the product of conception reach the 

 placenta is still obscure. The protein may be merely the 

 " circulating protein " found in the non-pregnant condition, or 

 more highly elaborated. The diffusion of the blood-sugar to 

 the foetus is disputable, 4 and the form of the fats is unknown. 

 Of the waste products carbonic acid, which, according to Bohr, 5 



1 Marshall and Jolly, "The Ovary as an Organ of Internal Secretion," 

 Phil. Trans., Roy. Soc., London, B., vol. cxcviii., 1905. 



2 Cramer (H.), "Transplantation menschlicher Ovarien," Munch, med. 

 Woch., 1906. 



3 With regard to the existence of an ovarian stimulus, see also Hilde- 

 brandt (Hofmeister's Beitrage, vol. v., 1904). * See Chap. X., p. 434. 



5 Bohr, " Der respiratorische Stoffwechsel des Saugetierembryo," Skand. 

 Arch. d. Phya., vol. x., 1900 ; also vol. xv., 1904. 



