CHAP, in.] THE NUTRITION OF THE EMBRYO. 677 



Concerning the rise and development of the functional activities 

 of the embryo, our knowledge is almost a blank. We know 

 scarcely anything about the various steps by which the primary 

 fundamental qualities of the protoplasm of the ovum are differen- 

 tiated into the complex phenomena which we have attempted in 

 this book to expound. We can hardly state more than that while 

 muscular contractility becomes early developed, and the heart 

 probably, as in the chick, beats even before the blood-corpuscles 

 are formed, movements of the foetus do not, in the human subject, 

 become pronounced until after the fifth month; from that time 

 forward they increase and subsequently become very marked. 

 They are often spoken of as reflex in character ; but only a pre- 

 conceived bias would prevent them from being regarded as largely 

 automatic. The digestive functions are naturally, in the absence 

 of all food from the alimentary canal, in abeyance. Though 

 pepsin may be found in the gastric membrane at about the fourth 

 month, it is doubtful whether a truly peptic gastric juice is 

 secreted during intra-uterine life ; trypsin appears in the pancreas 

 somewhat later, but an amylolytic ferment cannot be obtained 

 from that organ till after birth. The date however at which these 

 several ferments make their appearance in the embryo appears to 

 differ in different animals. The excretory functions of the liver 

 are developed early, and about the third month bile-pigment and 

 bile-salts find their way into the intestine. The quantity of bile 

 secreted during intra-uterine life, accumulates in the intestine and 

 especially in the rectum, forming, together with the smaller secre- 

 tion of the rest of the canal, and some desquamated epithelium, 

 the so-called meconium. Bile salts, both unaltered and variously 

 changed, the usual bile pigments, and cholesterin, are all present 

 in the meconium. The distinct formation of bile is an indication 

 that the products of foetal metabolism are no longer wholly carried 

 off by the maternal circulation ; and to the excretory function of 

 the liver there are now added those of the skin and kidney. The 

 substances escaping by these organs find their way into the 

 allantois or into the amnion, according to the arrangement of the 

 foetal membranes in different classes of animals; in both these 

 fluids urea or allied bodies have been found as well as the ordinary 

 saline constituents ; the latter may or may not have been actually 

 secreted. From the allantoic fluid of ruminants the body allan- 

 toin has been obtained, and human and other amniotic fluids have 

 been found to contain urea. It is maintained by some however 

 that the fluid in the amnion is secreted by the mother and that 

 hence the substances present in it are of maternal origin. 



About the middle of intra-uterine life, when the foetal circula- 

 tion is in full development, the blood flowing along the umbilical 

 vein is carried chiefly by the ductus venosus into the inferior vena 

 cava and so into the right auricle. Thence it is directed by the 

 valve of Eustachius through the foramen ovale into the left 



