522 THE PHYSIOLOGY OF REPRODUCTION 



and palpitation and by changes in the rate and rhythm of the 

 heart. An increased area of dulhiess to the right of the sternum 

 can usually be made out, but it is mainly due to the abnormally 

 transverse position of the heart, and to its greater contact with 

 the anterior wall of the chest (v. Winckel ^). 



It has been suggested that the increased work of the heart, 

 which leads in many cases to the dilatation of its chambers 

 and perhaps to some compensatory hypertrophy, is due to an 

 increased peripheral resistance from the presence of a vaso- 

 constricting substance in the blood.^ In excess it may cause 

 anuria and eclampsia (Nicholson *). 



The blood-pressure is not affected in normal pregnancy, 

 but is always raised in labour as a result of the uterine con- 

 tractions. After parturition the pressure falls, but rises again 

 on the third day of the puerperium. 



Varices of the lower extremities and external genitals are 

 frequent in human pregnancy. They are due mainly to the 

 increased intra-abdominal pressure and the stretching of the 

 abdominal wall. Secondary thromboses are common in the 

 puerperium. 



c. The Dudthss Glands. — There is regularly a sweUing of the 

 thyroid gland in pregnancy (Tait *), which consists of a simple 

 hypertrophy, and not a vascular engorgement or cystic change 

 (Freund ®). It has been shown experimentally in cats that a 



' V. Winckel, toe. cit., vol. 1., H. 1. This has been clearly established 

 by radiograms of the thorax in pregnancy. 



' The origin of this substance, if such exists, is still unknown. The 

 investigation of extracts of the placenta by the writer, in conjunction with 

 Dr. W. Cramer, proved that this organ contained no blood-pressure raising 

 substance. The substances extracted by Dixon and Taylor (" On the Physio- 

 logical Action of the Placenta," Proc. Roy. Soc. of Med., London, vol. i., 

 1908) from the placenta and observed to have an adrenalin-like action, 

 were subsequently shown to arise in the course o£ putrefaction (see Rosenheim, 

 Joum. ofPhys., 1909). 



' Nicholson, "The Maternal Heart in Pregnancy," Brit. Med. Joum., 

 1904, part ii. 



* Tait, " Enlargement of the Thyroid Body in Pregnancy," Obstet. Joum., 

 1875. 



^ Freund, " Ueber die Beziehung der Schilddriise," &c., Deuts. Zeitschr. 

 f. Chir., vol. xxxi., 1890. 



