528 THE PHYSIOLOGY OF REPRODUCTION 



observations on foiir pregnant dogs, though carried out a few years 

 after the publication of Bar's work, were completed without any 

 knowledge of it. They led to essentially the same conclusion, namely 

 that pregnancy is not necessarily associated with a loss of nitrogen 

 by the maternal organism and does not therefore entail a sacrifice on 

 the pai-t of the mother — " a sacrifice on the part of the individual for 

 the good of the species " — as the earher observers had believed; On 

 a suitable diet the mother may actually have retained considerable 

 amounts of nitrogen at the end of pregnancy. The nitrogen retention 

 does not, however, proceed evenly throughout pregnancy. Both in 

 Murlin's and in Bar's animals it was most pronounced when one 

 would least expect it, namely in the second half of pregnancy, when 

 the demands of the fcetus are greatest. Tliis^ increased nitrogen 

 retention is associated with a diminished nitrogen excretion in the 

 urine. In the first half of pregnancy the nitrogen retention is. much 

 less pronounced and there may actually be a nitrogen loss, indicating 

 an increased protein katabolism. 



Bar distinguishes, therefore, in the pregnant dog two distinct 

 periods of about equal length. The first period, when the needs of 

 the embryo in nitrogen are small, is characterised by a tendency to 

 loss of nitrogen on the part of the mother. This lasts to the middle 

 of pregnancy (the thirtieth day in the dog) when the second period of 

 distinct nitrogen retention sets in. Bar has noted further that during 

 the first period gastro-intestinal disturbances occur in the dog, and 

 has made the interesting suggestion that this period of nitrogen loss 

 coincides with the period of morning sickness with women. Now in 

 the dog the placenta is fully matured at about the thirtieth day of 

 gestation, in human pregnancy it is fully developed at the end of the 

 fourth month. Further, Graefenberg ^ has. shown that the chorionic 

 villi of the human placenta during the first three months of pregnancy 

 contain a proteolytic enzyme, the seat of wliich he ascribes to the 

 Langhans cells. This ferment weakens during the fourth month and 

 disappears in the fifth. This, coupled with the fact that the serum of 

 pregnant women has a greatly increased content of anti-trypsin from 

 the beginning of pregnancy on, is taken to indicate that these 

 proteolytic enzymes pass into the maternal organism, which protects 

 itself by the formation of anti-trypsin. It has been suggested, 

 therefore, that the period of protein katabolism is due to the for- 

 mation of proteolytic enzymes by the developing trophoblast and 

 the passage of these enzymes into the maternal organism. When 

 the placenta is fully formed the passage of these enzymes into 



1 Graefenberg, "Der Antitrypsingehalt des miitterliclieii Bhitserums wahrend 

 der Schwangerschaft," Munchmiefr ined. TFoc/i., vol. Ivi., 1909 ; " Beitrage zur 

 Physiologie der Eieinbettung," Zeitsch.f. Oelmrtsh. v. Oyn., vol. Ixv., 1909. 



