FEEDING OF ANIMALS. 319 



a sense be said to be little more than an accumulation of MUk-pro- 

 reserve material from excess of food, milk is a special pro- ^.^. 

 duct of a special gland, for a special normal exigency of the pendent 

 animal. Further, whilst common experience shows that the ^^waion 

 herbivorous animal becomes the more fat, the more, within upon nitro- 

 certain limits, its food is rich in' carbohydrates, it points to 9 Jj™^ sub ~ 

 the conclusion that both the yield of milk, and its richness 

 in butter, are more connected with a liberal supply of the 

 nitrogenous constituents in the food. Obviously, so far as 

 this is the case, it may be only that thereby more active 

 change in the system, and therefore greater activity of the 

 special function, is maintained. The evidence at command 

 is, at any rate, not inconsistent with the supposition that a 

 good deal of the fat of milk may have its source in the break- 

 ing up of albuminoids, but direct evidence on the point is still 

 wanting ; and, supposing such breaking up to take place in 

 the gland, the question arises — what becomes of the bye- 

 products ? Assuming, however, that such change does take 

 place, the amount of nitrogenous substance supplied to the 

 Eothamsted cows would be less in excess of the direct re- 

 quirement for milk-production than the figures in the table 

 would indicate — if, indeed, in excess at all. 



The figures in the column relating to the estimated amount Non-nitro- 

 of digestible non-nitrogenous substance reckoned as starch, d^nous 



ii i • n i -1-ihr-iii matter for 



show that the quantity actually consumed was 11.71 lb., sustenance 

 whilst the amount estimated by Wolff to be required was andm ^ k - 

 12.5 lb., besides 0.4 lb. of fat. The figures further show that, 

 deducting 7.4 lb. for sustenance from the quantity actually 

 consumed, there would remain 4.31 lb. available for milk-pro- 

 duction, whilst only about 3.02 would be required supposing 

 that both the fat of the milk and the sugar had been derived 

 from the carbohydrates of the food ; and, according to this 

 calculation, there would still be an excess in the daily food of 

 1.29 lb. 



It is to be borne in mind, however, that estimates of the Variations 

 requirement for mere sustenance are mainly founded on the m / ood re - 

 results of experiments, in which the animals are allowed only for susten- 

 such a limited amount of food as will maintain them without ance - 

 either loss or gain when at rest. But physiological considera- 

 tions point to the conclusion that the expenditure, independ- 

 ently of loss or gain, will be the greater the more liberal the 

 ration ; and hence it is probable that the real excess, if any, 

 over that required for sustenance and milk-production, would 

 be less than that indicated in the table, which is calculated 

 on the assumption of a fixed requirement for sustenance for a 

 given live-weight of the animal. 



Supposing that there really was any material excess of 



