REPRODUCTION 873 



We may now give something more of precision to the statements 

 that different parts of the body receive blood of different quality ; 

 and it is possible roughly to divide the organs in this respect into 

 four categories : (i) The liver, which partakes both of the best and 

 the worst, the purified blood of the umbilical veins and the vitiated 

 blood of the intestines and spleen ; (2) the heart, head, and upper 

 limb;-, which receive the blood from the inferior extremities and 

 kidneys, mixed with the pure blood of the venous duct ; (3) the legs, 

 trunk, intestines, and kidneys, which are fed chiefly by the off- 

 scourings of the cephalic end, mitigated, however, by a proportion 

 of mixed blood from the inferior cava ; (4) the lungs, which receive 

 only a feeble stream of unmixed venous blood. 



These peculiarities of the embryonic circulation are in obvious 

 correspondence with the physiological events taking place in the 

 foetal body. The liver is not only the greatest gland in the embryo, 

 as it continues to be in the adult, but its activity seems to dwarf that 

 of all the other glands put together, and is in striking contrast with 

 the functional torpor of the lungs. From the third month of intra- 

 uterine life the secretion of bile begins and the intestines gradually fill 

 with meconiuni) of which the principal constituent is bile. Accord- 

 ingly the liver is most lavishly supplied with blood, while the lungs 

 are stinted. And since the liver has, as we have already learnt, 

 other and, in the adult at least, even more important labours than 

 excretion, a large portion of the blood it receives is of the best 

 quality : it enters the gland comparatively rich in oxygen, and passes 

 out comparatively poor ; while the lungs, which have to be nourished 

 only for their own sake, and are of no use whatever till the child is 

 born and respiration has begun, must be content with the poorest 

 fare with the crumbs that fall from the table of foetal nutrition. The 

 full-fed cephalic end of the embryo grows far more rapidly than the 

 half-starved inferior extremities, and the head of the riew-born child is 

 large in proportion to the rest of the body. 



There are some other points in the physiology of intra-uterine life 

 which call for remark ; and, to sum up in a few words the grand 

 distinction between foetal and adult life, we may say that growth is 

 the keynote of the former, work (functional activity) of the latter. 

 Thus, the muscles at an early period in their development become 

 the seat of a great accumulation of glycogen, an accumulation which 

 would entirely unfit them for the labours of fully-formed muscles, 

 but which seems to be intimately connected with their own growth, 

 and perhaps also with the growth of other tissues. Later on, when 

 the muscles have been formed, their powers still lie dormant, but for 

 the infrequent and feeble movements, generally regarded as reflex, 

 but possibly to some extent originated in the cerebral cortex, which 

 gives the mother the sensation of 'quickening.' But the store of 

 glycogen now becomes reduced to its permanent amount, and the liver 

 takes on its glycogenic function. It can hardly be doubted that 

 the glycogen found in the placenta (bitch) is also deposited there in 

 the interest of the rapidly growing foetal tissues, as a kind of current 

 account on which they can operate at any moment of emergency, 



