990 THE PHYSIOLOGY OF REPRODUCTION. 



show that the maternal fat is not transferred through the placenta. 

 In all probability the fetus synthesizes its own fat from the carbo- 

 hydrate material furnished to it by the mother. The body fat of 

 the fetus is at first slight in amount, but after the sixth month be- 

 gins 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. That the fiver also begins to as- 

 sume its functions early is shown by the fact that from the fifth 

 to the sixth month one may find bile in the gaU-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 

 QOt present at birth. In general, it is evident that for a long period 

 the maternal organism digests and prepares the food for the embryo, 

 excretes the wastes, regulates the conditions of temperature, etc., 

 as it does for a portion of its own substance, but as the fetus ap- 

 proaches term its tissues and organs begin to assume more of an 

 independent activity, as indeed must be the case in preparation 

 for the sudden change at birth. In this respect, as in all parts of 

 the reproductive process, we meet with regulations whose mechanism 

 is but dimly understood. 



Changes in the Maternal Organism during Pregnancy. — 

 The two most distinct effects upon the mother that result from 

 pregnancy are the growth of the uterus and of the mammary gland. 

 The virgin uterus is small and firm, weighing from 30 to 40 gms., 

 while at the end of pregnancy it may weigh as much as 1000 gms. 

 This great increase in material is due partly to the growth of new 

 muscular tissue and partly to an hypertrophy of the muscle already 

 present. In the uterus at term the muscle cells are much longer 

 and larger than in the organ before the implantation of the 

 fertilized ovum. The stimulus that initiates and controls this 

 new growth is seemingly the fertifized ovum itself, but the phys- 

 iological means employed are not comprehended. We know 

 from experiments upon lower animals (Rein) that when all 

 connections with the central nervous system are severed the 

 fetus develops normally and the uterus increases correspond- 

 ingly in size and weight. The influence of the ovum on the 

 uterus must be exerted, therefore, in all probability, through 



