874 A MANUAL OF PHYSIOLOGY 



when the more distant maternal reserves cannot be drawn upon 

 in time. 



The excretory glands of the embryo, except the liver, scarcely 

 awaken to activity during foetal life. Urine may, indeed, be some- 

 times found in the bladder at birth, but it is often absent: and 

 although a portion of the amniotic fluid, which contains traces of 

 urea and salts, in addition to small quantities of albumin, may be 

 secreted by the renal tubules, and find its way through the still 

 open urachus into the amniotic sac, this contribution cannot imply 

 more than a very slight degree of glandular action. The experi- 

 ments of Kuntz, indeed, go far to show that this liquid comes 

 essentially from the mother rather than from the child. He found 

 that sulphindigotate of sodium injected into the bloodvessels of a 

 pregnant animal (sheep) coloured the amniotic fluid and the 

 placental tissues, but not the foetus; while after injection into the 

 latter the foetal kidneys contained particles of the pigment, while the 

 amniotic fluid remained uncoloured. The sebaceous glands have 

 certainly begun their work by the secretion of the vernix caseosa, an 

 oily material which covers the skin and serves to protect it from the 

 continual irritation of the fluid in which the embryo floats. 



The nervous system is even less active than the glandular tissues, 

 and not more active than the muscles. There is evidently no scope 

 for the exercise of the special senses. Psychical activity of every 

 kind must be at the lowest ebb. Consciousness, if it exists at all, 

 must be dull and muffled. And if motor impulses are discharged 

 from the cortex, the psychical accompaniments of such discharge are 

 doubtless widely different from those which we associate with volun- 

 tary effort. 



This functional calm, broken only by the beat of the heart, is 

 accompanied by a very feeble metabolism. The amount of oxygen 

 carried to the tissues of an embryo sheep weighing 3*6 kilos, by the 

 blood of the umbilical vein, was only 1-7 c.c. per minute; 2-8 c.c. of 

 carbon dioxide per minute was given up to the blood of the mother 

 in the placenta (Kuntz and Cohnstein). The gaseous exchange was, 

 therefore, not one-tenth as much as in the adult sheep. In fact, the 

 heat-production of the foetus, sheltered as it is from loss except by 

 the placental circulation, is only sufficient to raise its temperature by 

 a small fraction of a degree above that of the mother. And it is not 

 difficult to see that a large portion of this production must be due to 

 the action of the heart. This beats at the rate of about 140 times a 

 minute at full term * The blood-pressure in the umbilical artery of 



* It has not been finally determined whether the rate of the heart 

 varies v/ith the size, or what probably comes to the same thing, with the 

 sex of the foetus. As we have seen, the variation of the rate in the adult 

 with the size of the body is associated with a corresponding variation in 

 the metabolism and heat-loss, which are proportionally greater in a small 

 than in a large animal. If this is a causal connection we should not 

 expect that in the embryo in utero, where the conditions as regards heat- 

 loss are entirely different, such a relation should exist, at any rate within 

 the same species. 



