44 A SftKfi/ of Xifrof/en Metabolmn in the JJnirij Cow 



70 days. In tliis particular, therefore, our scheme of experiiuent would 

 appear to have been defective in that the change of ration from period 

 to period was evidently made before the influence of the earlier ration on 

 nitrogen-retention had been exhausted. Accordingly, before proceeding 

 further with the comprehensive programme of experimental work on 

 these lines which lay before us, we thought it desirable to make a more 

 prolonged study of nitrogen-retention under conditions of roughly con- 

 .staiit nitrogen-consumption, and a further experiment was undertaken 

 in November, 1917, and developed later into a study of nitrogen-retention 

 during pregnancy and lactation, the whole experiment covering a period 

 of two years. 



SECOND EXPERLAIEXT. 



(November, 1917 — November, 1919.) 



(icneral Plan of Experiment. 



Two Siiorthorn cows, C and D, similar to those used for the first 

 experiment, both "dry" and not in calf, were weighed and placed on a 

 daily ration consisting of 20 lb. "seeds" hay. The nitrogen-balance in 

 both cows was followed continuously, except for the one week monthly 

 during which the cows were weighed and an interval of 10 weeks 

 at the end of the first year. After a period of 302 days (including 

 255 days for which the nitrogen-balance records were obtained) during 

 which both cows received identical treatment. Cow D was put to 

 the bull, whilst Cow C remained unserved as control. The nitrogen- 

 balance measurements were continued for both cows tjiioughout the 

 period of jjregnancy of Cow D and subsequent parturition, and were 

 further extended well into the period of lactation. For Cow D the experi- 

 ment extended over periods of 302 days "dry"' and not in calf, 2Sf davs 

 "dry" but in calf, and 136 days in milk, a total of 722 day.s throughout 

 the whole of which period Cow C was maintained dry and not in calf. 

 Samples for nitrogen-balance determinations were taken on 54() days 

 during this period. 



Both this and the foregoing experiment were carried out in a building 

 specially designed for work of this character. The floor was of cement, 

 graded and grooved to secure ra]>id drainage, each cow-stall being pro- 

 vided with a separate drain, so arranged that the drainage could be easily 

 collected for purposes of weighing and sampling. Preliminary tests 

 showed that any liquid falling on the floors of the stalls could be recovered 

 within 2 or 3 per cent., whilst by spraying the floors occasionally with 



