48 A Study o/yitrugen Metaholisin in t/ic Ddirij Cow 



this seems to have passed away ((uickly and between days 219 and 257 

 iiitiogeii-eqiiilibriuin again prevailed. Thus, but for the abnormal period 

 of days 198-215, e(juilibrium was maintained over a period of 164 days. 

 It was all the more surprising therefore in the subsequent periods from 

 day 261 to day 295 to tind that nitrogen storage was again taking place, 

 a phenomenon of which the explanation is not very ob^aous. It certainly 

 cannot be attributed to more than a small extent to the comparatively 

 small rise in nitrogen-consumption in the ])eriod of days 261-278. 



The record of Cow D is very similar for the first part of the period, 

 the nitrogen-retention falling steadily until the 100th day or thereabouts 

 when nitrogen-equilibrium was established. The jjeriod from the 114th 

 to the 131st day shows an almost perfect nitrogen-balance, but subse- 

 quently a curiously persistent small retention of nitrogen was recorded 

 throughout the remaining 164 days, increasing appreciably, as in the 

 case of Cow C, in the last stages of the period. 



Over the whole period, out of 37-6 kg. nitrogen consumed by each 

 cow, Cow C retained 8(i() gm. and Cow D 1571 gm., whilst the gains in 

 live-weight were 109 lb. and 118 lb. respectively. 



No clear correlation is evident between the nitrogen-balances and the 

 weight changes. For instance, between days 114 and 131, Cow C showed 

 a daily negalire nitrogen-balance of 2-6 gm. and an Increase in weight of 

 30j lb. for the period. Between days 72 and 89, however, where the cow 

 f/ained 2-6 gm. of nitrogen daily, the weight of the cow suffered a loss of 

 3?5 lb. for tiie period. 



The extremely irregidar variation of the figures in the nitrogen- 

 balance and weight columns, and the disconcerting rise in the nitrogen- 

 retention after 240 days of relatively uniform feeding, show clearly the 

 danger of placing too much reliance on conclusions drawn from the results 

 of short-perjod experiments with cattle. A three-weeks' period in work 

 of this character is obviously far too short. 



Comments on Table IV (Second Main Period of Experiment). 



Cow D was put to the bull on September 6, 1918 (day 303), and the 

 measurements of the nitrogen-balances were suspended until November 

 8, 1918 (day 366), This break in the measurements was unfortunate, 

 since, on resumption of the trials, distinct indications were obtained 

 that the protein metabolism of Cow D had undergone a marked dis- 

 turbance in the early stages of pregnancy. Up to day 295, Cow D had 

 shown throughout a uniforndy higher positive nitrogen-balance than 

 Cow C. On resumption, however, Cow D was found to be distinctly in 



