174 MA'NUAh OF CATTLE-B^ERDJNa. 



serve for tlie production of fat only wlien the protein and 

 fat of the food were exhausted, or, in other words, when 

 the snpply of oxygen in the body was not sufficient to con- 

 sume all the carbhydrates. If we find that, in all experi- 

 ments on fattening, the digestible protein and fat of the 

 food are sufficient to account for the amount of flesh and 

 fat actually produced, we shall have very strong presump- 

 tive evidence that the views of Voit & Pettenkofer and 

 their followers are correct, though, of course, such evi- 

 dence is of a negative character and can never reach abso- 

 lute proof. If, on the other hand, we find that, in ac- 

 curately conducted experiments, the digestible protein and 

 fat of the food do not suffice to account for the flesh and 

 fat produced within the limits of experimental error, we 

 have a proof that the carbhydrates of the food must have 

 contributed to its formation to the extent, at least, of the 

 observed difference. 



Experiments on RuminaBts.— Unfortunately there 

 have been as yet no extensive investigations in which the 

 fat-production of domestic animals, or of ai^y herbivorous 

 animals, under the influence of a definite and suitable ra- 

 tion, has been determined with scientific accuracy, i e,, by 

 careful determination of all the solid, liquid, and gaseous 

 excretions. 



In considering this question, we can avail ourselves 

 only of the results of so-called " practical " experiments, 

 in which the nutritive effect of the fodder has been de- 

 termined simply by the increase of the live weight of the 

 animal, or perhaps from the dressed weight, or at best 

 from experiments in which the "sensible" (solid and liq- 

 uid) but not the gaseous excretions have been accurately 

 determined. 



Milk-fat — In regard to the production of milk-fat by 



