loi6 A MANUAL OF PHYSIOLOGY 



and the head of the new-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, long before 

 any glycogen can be found in the liver, become the seat of an accumu- 

 lation of glycogen, which, since it cannot be used up in contraction 

 as in the adult muscles, seems to be intimately connected with their 

 own growth, and perhaps also with the growth of other tissues. Tt is 

 true that the foetal tissues as a whole, including the muscles, are not 

 richer, as used to be taught, but poorer in glycogen than adult 

 tissues, and therefore the old doctrine that the foetal glycogen fulfils 

 a special ' formative ' function in the development of the tissues, 

 has lost its experimental basis. Nevertheless, there is a paral- 

 lelism between the growth of the foetus and its glycogen content. 

 In cases where the growth of the foetus has been spontaneously 

 arrested, the percentage amount of glycogen in its organs has been 

 found to be diminished out of proportion to the diminution in weight. 

 A similar retardation of development can be produced by repeatedly 

 injecting phloridzin into the mother, and thus reducing the glycogen 

 store of the foetus (Lochead and Cramer). Probably, then, the foetal 

 glycogen assists the growth of the embryo, which is known to be 

 accompanied by an intense carbo-hydrate metabolism, by furnishing 

 a store of easily oxidized material for the nutrition of the developing 

 tissues. When the muscles have been formed, their glycogen is 

 still consumed in growth, and their functional powers lie dormant, 

 but for the infrequent and feeble movements, generally regarded as 

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

 which give the mother the sensation of ' quickening.' It is only 

 late in development that the embryonic liver takes on its glycogenic 

 function. In the earlier stages it is entirely free from glycogen. It 

 is an interesting illustration of that exact adaptation of means to 

 ends which so constantly impresses the investigator of the animal 

 mechanism that the ferment which converts glycogen into dextrose 

 (glycogenase) is also either entirely absent from the liver early in 

 gestation, or present only in traces ; and that as the glycogen-forming 

 and glycogen-storing functions of the organ increase in importance, it 

 becomes richer in glycogenolytic ferment. It cannot be doubted that 

 the glycogen found in the placenta is also deposited there in the interest 

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

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

 when the more distant maternal reserves cannot be drawn upon in 

 time. The glycogen is formed in the placenta, probably from the 

 dextrose of the maternal blood. By means of a glycogen-splitting 

 ferment, which can be extracted by glycerin from the placenta, the 

 glycogen appears to be reconverted into dextrose for absorption by 

 the foetus. In the earlier period of gestation the placenta seems 

 to perform vicariously the glycogenic function of the liver, and as 

 the glycogen content of the liver increases in the later stages of intra- 

 uterine life, that of the placenta diminishes proportionally. 



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. It is a 

 dilute urine, with a molecular concentration only about half as great 



