FEEDING OF ANIMALS. 289 



ference, that is, the amount of carbon available from the nitro- 

 genous substance for the formation of fat, more or less than 

 that required for the amount of fat produced. 



Then, in the bottom division of the table are shown, for 100 

 of carbon in the estimated produced fat — the amount available 

 from the nitrogenous substance, and the amount not available 

 from that source, in each experiment; the amount not so 

 available representing, of course, the proportion required from 

 other sources. 



It is hardly necessary to point out, that according to the 

 above mode of illustration, the figures show, not only the ut- 

 most proportion of the stored up fat which could possibly have 

 had its source in the nitrogenous substance of the food, but 

 notably more than could possibly have been so derived. 

 Thus, to say nothing of other considerations, it has been as- 

 sumed, for simplicity of illustration, and for the sake of 

 argument, that the whole of the nitrogenous substance of the 

 food not stored up as increase would be perfectly digested, 

 and be available for fat-formation ; and that, in the breaking 

 up of the nitrogenous substance for the formation of fat, no 

 other carbon compounds than fat and urea would be produced ; 

 and lastly, that the whole of the ready-formed fatty matter of 

 the food has contributed to the fat stored up. It is obvious, 

 however, that these assumptions are in part improbable, and in 

 part quite inadmissible ; whilst the tendency of the error is, in 

 each case, to show too large a proportion of the stored up fat 

 to have been possibly derived from the ready-formed fat, and 

 the nitrogenous constituents, of the food. 



It is obvious, therefore, that where the figures show an Amount of 

 excess of carbon available from nitrogenous substance over /^^"^ 



TTOIYb Oth/QT 



that which would be required if the produced fat had been sources 

 formed from it, the excess is over-estimated; and, on the-^f*^ 

 other hand, that where they show a deficiency of nitrogenous .figures 

 substance for such formation, the deficiency is under-esti- show - 

 mated ; so that, in fact, the amount of fat required to be de- 

 rived from other sources would be greater than the figures 

 indicate. Indeed, according to the mode of calculation 

 adopted, 100 of nitrogenous substance would yield 62 parts 

 of fat ; but it has been fully admitted in subsequent discus- 

 sions, that at most 51.4 parts of fat could possibly be derived 

 from 100 parts of proteid substance; and more recently a 

 much lower figure has been adopted. 



After these general remarks, we may now turn to the con- Results. 

 sideration of the results of the different experiments. 



In experiment 1, two pigs of the same litter, of almost ex- 

 actly equal weight, and, as far as could be judged, of similar 

 character, were selected. One was killed at once, and the 



VOL. VII. T 



