PREGNANCY AND PARTURITION 1379 



small. It is protected from all loss of heat, movements are sluggish 

 or for the most part absent, and the only oxidative processes are 

 those required in the building up of the developing tissues. On the 

 other hand, the foetus has need of a rich supply of food-stuffs, which it 

 must obtain through the placental circulation. It is imagined that the 

 epithelium covering the villi serves as an organ for passing on the 

 necessary food-stuffs from the maternal to the foetal blood in the form 

 best adapted for the requirements of the fcetus. We know, however, 

 practically nothing as to the changes or mechanism involved in this 

 transference. Although most of the organs of the foetus are fully 

 formed some time before birth, they are for the most part in a state of 

 suspended activity. The nitrogenous excreta are turned out by 

 the placenta, so that the fcetal secretion of urine is minimal or absent. 

 The alimentary apparatus is for the most part ready. Thus pepsin can 

 be extracted from the fcetal gastric mucous membrane. The pancreas 

 contains trypsinogen and the intestinal mucous membrane pro- 

 secretin. Amylolytic ferments seem, however, to be absent both from 

 the salivary glands and the pancreas. The liver stores up glycogen 

 and secretes bile, which accumulates in the small intestine, forming 

 the ' meconium.' This is generally voided by the child shortly after 

 birth. 



THE FCETAL CIRCULATION. In the fcetus, from the middle of 

 intra-uterine life, we find certain arrangements of the circulation which 

 are directed to providing the fore part of the body, especially the rapidly 

 growing brain, with oxygenated blood, while the less important tissues 

 of the limbs and trunk receive venous blood (Fig. 563). The arterial 

 blood coming from the placenta along the umbilical veins can pass 

 directly into the liver. The greater part of it, however, traverses the 

 ductus venosus to enter the inferior vena cava, by which it is carried to 

 the right auricle. Here it impinges on the Eustachian valve, and is 

 directed thereby through the foramen ovale into the left auricle, whence 

 it passes into the left ventricle to be driven into the aorta. As this 

 arterial blood passes into the inferior cava, it is of course mixed with 

 the venous blood, returning from the lower limbs and lower part of 

 the trunk. By the aorta this mixture, containing chiefly arterial 

 blood, is carried to the head and fore limbs. The venous blood from 

 these parts is carried by the superior vena cava to the right auricle, 

 and thence to the right ventricle, by which it is driven into the pul- 

 monary artery. Only a small part of the blood, however, passes 

 through the lungs, the greater part traversing the patent ductus 

 arteriosus to be discharged into the aorta below the arch, whence it 

 flows partly to the lower limbs and trunk, but chiefly to the placenta 

 by the umbilical arteries. In the fcetus therefore the work of the 

 circulation is largely carried out by the right ventricle. The greater 



