530 THE PHYSIOLOGY OF REPRODUCTION 



health and enables them to grow and to breed. On this diet the mother 

 just managed to maintain its weight at the end of pregnancy. But when 

 this diet is supplemented by yeast preparations which are rich in the 

 water-soluble vitamin, then the mother always showed a considerable 

 gain of weight during pregnancy. The weights of the foetus were not 

 affected. These observations show very clearly the importance of an 

 abundant supply of vitamin during pregnancy for the protection of 

 the maternal organism. They also demand a repetition of the 

 metabolism experiments on dogs with an abundant supply of 

 vitamins in the food, before it can be accepted as definitely established 

 that a period of increased protein breakdown is a regular feature of 

 the early period of pregnancy. What can be regarded as definitely 

 established is the fact that the maternal organism is capable of 

 adapting itself to the requirements of the growing foetus, and that this 

 adaptation is so efficient that the maternal organism itself gains by it. 



This remarkable retention of nitrogen during pregnancy is 

 probably a preparation for the period of lactation. The energy 

 requirements of the new-born are, as Murlin showed, very much 

 higher than those of the embryo immediately before birth. This is 

 due to the fact that the new-born has to maintain its body tempera- 

 ture against a colder environment. In Cramer's experiments on 

 rats it was found accordingly that the mother, who has to provide 

 for a litter of six to nine young ones, always loses in weight con- 

 siderably during the period of lactation, even when the diet is very 

 rich in vitamins. But in the latter case this loss does not exceed the 

 gain in weight acquired during pregnancy. On a diet more restricted 

 in vitamins the weight of the mother at the end of lactation was 

 always considerably below that at the time of conception. These 

 findings suggest the possibility that in the human subject the supply 

 of vitamins may be a factor determining the capacity to nurse. 



In the human female a nitrogen retention has been found 

 frequently. Most of these observations could be carried out only 

 during the last few weeks of pregnancy. The careful and complete 

 observations of Zacharjewsky ^ during the last few days of pregnancy 

 are the first contribution to the problem. He found a gain of 

 nitrogen of 0'873 gm. per diem in primiparte and 5'05 gm. in 

 multiparte. Similar results were obtained by Schrader,^ by Moris 

 Siemens,^ and by Hahl.* Observations during the earlier periods of 



' Zacharjewsky, " Uber den Stickstoifweclisel wahrend der letzten Tage der 

 Schwangerschaft," Zeitsch. f. Biol. N.F., vol. xii., 1894. 



2 Scnrader, "IJntersuchungen fiber den StofFwechsel wahrend der Schwanger- 

 5 schaft und im Wochenbett," Arch. f. Gynah, vol. Ix., 1900. 



^ Slemons, loc. at. 



* Hahl, " Beitrage zur Kenntniss des Stoffwechsels wahrend der Schwanger- 

 Bchaft," Aroh.f. Oyniih., vol. Ixxv., 1905. 



