526 THE PHYSIOLOGY OF REPRODOCTION 



Hagemann's^ investigations in the dog forfii the first accurate 

 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 gm. nitrogen were retained, the young 

 contained at birth 7'445 gm. This left a balance of 26-128 gm.for 

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

 for the formation of the foetuses (calculated at 16"6 gm.) and placentae 

 (8'7 gm.). 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 gni. nitrogen were retained, and the 

 calculated excretion in the milk was 76 gm. — a loss of 41 '944 gm. 

 nitrogen. 



Later work has shown that this conclusion is not warranted, but 

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

 difficulties 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 gm. 

 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. 



On one point the results are of value. Hagemann states that the 

 period of gestation may be divided into two parts. In the first, 

 which lasts in his experiment for the first month of pregnancy, there 

 ' is a continuous loss of nitrogen to the mother each day. In the 

 second, there is a storage of nitrogen which is used in the growth of 

 the product of conception. 



In Ver Eeke's experiments, nineteen in all, on the rabbit, two 

 phases were also frequently observed, but the results varied widely. 

 In some there was a positive balance throughout, and in others a 

 negative balance now at one time and now at another. In the 



'Hagemann, "Ueber Eiweissumsatz wahrend der Sehwangerscliaft und 

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

 Erlangen, 1891. 



^ Ver Eeke, Lois des echanges nntritifs pendant la gestation, Bruxelles, 1901. 



^ Bar and Daunay, "Bilan des echanges azotes pendant la grossesse," Jour, 

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



