33 



constitaeDts can be produced, aud tlius the digestible portions of the 

 straw can be utilized. 



Such experiments as have been described have given an insight into 

 the atiiountsaud proportions of these dififerentconstituents which a ration 

 should contain in order to be the most economical in feeding, in order 

 to give the largest amount of product in the form of meat, milk, or labor 

 from the smallest amount of raw material in the form of food. 



Knowingthe amount of digestible albuminoids, carbohydrates,fat, &c., 

 which the animal requires, and the amount of these which each kind of 

 food will furnish, we can calculate what amounts and mixtures of the 

 fodder we have will be most profitable in feeding our stock. Scores of 

 tables of fodder-mixtures, giving amount and proportions of the more 

 common fodder materials suitable to different animals under different 

 circumstances, have been made out by the experimenters. They are 

 published in a great variety of forms, and many thousands of German 

 farmers can from actual experience testify to their value. 



In the experiments thus far described, no data are obtained for the 

 direct determination of the ways in which the various constituents of 

 the food are assimilated and used in the animal body. A partial solu- 

 tion of this problem, the discovery of the laws of flesh-building, is 

 sought in — 



3d. Feeding experiments in which, in addition to the food and excre- 

 ment, the quantity and composition of the urine are also determined, 

 with a view to learning the laws of flesh building in the animal body. 

 The great importance of these experiments depends upon the fact that the 

 nitrogen in tbe urine comes from the transformation of the albuminoid 

 constituents (flesh) of the animal body, and that under normal circum- 

 stances the amount of the nitrogen in the urine is an accurate measure of 

 the transformation ot these substances. If, therefore, on comparing from 

 day to day the amount of nitrogen in the urine with that in the food di- 

 gested, we Irnd a deficit, we inter that it has been retained in the body, 

 or, in other words, that the amount of tlie albuminoid mattersof the food 

 that has been stored away as flesh is greater than the amount of flesh 

 consumed. If, on the other hand, the amount of nitrogen in the 

 urine is more than was digested from the food, the inference is that the 

 store of flesh in the body is decreasing. We have, therefore, in experi- 

 ments of this sort a means of determining whether, under the influence 

 of a given food-ration, there is from day today an increase or diminution 

 • in the store of flesh in the animal body. We have thus a means of tell- 

 ing what are the effects of different food -materials on the building of 

 flesh in the animal body. 



An iuipoitant and much-vexed question at the present is, Of what 

 constituents of the food is the fat in the body built up ? The solution of 

 this, as well as of the more general question, as to what are the functions 

 of the different constituents of the tbod, albuminoids, fats, carbohy- 

 drates, and crude fiber and mineral matters in the animal economy, is 

 sought in — 



4th. Experiments which give as results complete data for computing 

 the amount of transtormation of these different substances in the animal 

 body, in that measurements and analyses are not confined to the food 

 consumed on tlie one hand, and the excrement and urine produced there- 

 from oft the other, but also, by means of a resinration apparatus, are ex- 

 tended to the remaining and otherwise undetermined products of these 

 transformations, to wit, the gases given off' by respiration through the 

 lungs and skin. 



The first successful respiration apparatus was that deviled by Petten- 

 o A 



