500 THE PHYSIOLOGY OF REPRODUCTION 



creased and katabolic processes decreased in pregnancy in dogs, 

 rabbits, and guinea-pigs. 



Hagemann's 1 . investigations in the dog form the first ac- 

 curate observations of the nitrogen balance during the whole 

 course of pregnancy. He set himself to solve the question 

 whether the new organism was formed from the food, or at the 

 expense of the maternal tissues. From the first experiment he 

 concluded that, even on a diet rich in nitrogen, there was a loss 

 of protein to the mother at the end of pregnancy. While 

 33'583 grm. nitrogen were retained, the young contained at 

 birth 7'445 grm. This left a balance of 26-128 grm. for the 

 extra needs of the mother, which, he says, was nearly all 

 required for the formation of the foetuses (calculated at 

 16-6 grm.) and placentae (8'7 grm.). The additional nitrogen 

 required for the growth of the uterus and mammae must have 

 been derived from the maternal tissues. Hence the pregnancy 

 resulted in a loss to the mother. Similarly in lactation 

 34-056 grm. nitrogen were retained, and the calculated excretion 

 in the milk was 76 grm. — a loss of 41-944 grm. nitrogen. 



It is doubtful if such a conclusion is warranted, but the 

 figures have been given in some detail to illustrate some of the 

 difiiculties to be overcome in carrying out the investigation. 

 Many troubles have been experienced in trying to keep the 

 animals on a constant diet, and, in addition, the increasing size 

 of the uterus may prove a mechanical difficulty and impede 

 the intestinal activity (Ver Eeke ^). Hagemann failed to obtain 

 the shed placentae, which were eaten by the mother animal. 

 Hence the estimate of 8-7 grm. nitrogen lost by them during 

 pregnancy and labour is arbitrary, and is, according to Bar and 

 Daunay,^ much too high. On these and other grounds — ^there 

 is a period of thirteen days during the pregnancy for which 

 no data are given — the calculations for pregnancy considered 

 as a unit are open to objection. 



^ Hagemann, " TJeber Eiweissumsatz wahrend der Schwaugersohatt und 

 Laktation," Arch, f. Anat. u. Phys., phys. Abth., 1890; also Inaug. Diss., 

 Erlangen, 1891. 



^ Ver Eeke, Lois des echanges nutriiifs pendant la gestation, Bruxelles, 

 1901. 



3 Bar and Daunay, ' ' Bilan des echanges azotes pendant la grossesse," 

 Joum. de Phys. et de Path., vol. vii., 1905. 



