THE FEMALE REPRODUCTIVE ORGANS. 853 



tioning, in fact, in much the same way as the intestinal villi. This 

 assumption implies that the epithelial cells of the villi take an active 

 part in the absorption of material by virtue of activities which can 

 not be wholly explained, but which without doubt are due to the 

 chemical and physical properties of the substance of which they are 

 composed. This assumption does not mean that the simpler 

 and better understood physical properties of diffusion and osmosis 

 are not also important. The respiratory exchange of gases, the 

 diffusion of water, salts, and sugar, may be largely controlled in this 

 way. There are no facts at least which contradict such an assump- 

 tion. The passage of fats and proteids, however, would seem to 

 require some special activity in the chorionic tissue, which may be 

 connected with the presence of special enzymes. Glycogen occurs 

 in the placenta itself and in all the tissues of the embryo during the 

 period of most active growth. In the later period of embryonic 

 life, as the liver assumes its functions, the glycogen becomes 

 more localized to this organ and disappears, except for traces, 

 in the skin, lungs, and other tissues in which it was present at 

 first in considerable quantities. It would appear, therefore, that 

 glycogen (sugar) represents one of the important materials for the 

 growth of the embryo, and that in the beginning at least the tissues 

 generally have a glycogenetic power. The sugar brought to the 

 placenta in the maternal blood passes over into the fetal blood and 

 the excess beyond that immediately consumed is deposited in the 

 tissues as glycogen. The body fat of the fetus is at first slight in 

 amount, but after the sixth month begins to increase with some 

 rapidity. The fat-forming tissues are in full activity, therefore, 

 before birth, and function doubtless in the same way as in 

 the adult. Before birth also the various organs begin to take on 

 their normal activity. The kidney may form urine long before 

 birth, as is shown by the presence of this secretion in the bladder, 

 and, shortly before birth at least, it has the power of producing 

 hippuric acid, as may be shown by injecting benzoates into the 

 blood of the mother. The kidney functions of the embryo, how- 

 ever, are doubtless performed chiefly by the placenta and the 

 kidney of the mother up to the time of birth. That the liver also 

 begins to assume its functions early is shown by the fact that from 

 the fifth to the sixth month one may find bile in the gall-bladder. 

 In the intestine, colon, there is found also a collection of excrement, 

 the meconium, which shows that the motor and secretory functions 

 of the intestinal canal may be present in the last months of fetal 

 life. From the pancreas a proteolytic enzyme may be extracted at 

 the time of birth or before, but the amylolytic enzyme is not formed 

 apparently until some time later. It is stated, at least, that it is 

 not present at birth. In general, it is evident that for a long period 



