of the Fat of the Animal Body. 445 



In fact, from the very opposite characters of the ruminant in 

 these respects, it is very much less appropriate for the purpose 

 of estimating the sources in its food of the fat of its body. It 

 is true that there is the advantage with the cow, that that im- 

 portant product of the food — the milk — is collected externally 

 to the body, and hence its amount and composition can be easily 

 determined; but the changes of weight of the animal itself, 

 though comparatively small, are due to a greater variety of cir- 

 cumstances, and can, therefore, with less of certainty be properly 

 interpreted than even in the case of either the ox or the sheep. 

 Indeed, when experiments are conducted with cows or oxen, or 

 even with sheep, for periods of a few w r eeks only, the variation 

 in live-weight may in very great proportion be due to variation 

 in the contents of the alimentary organs merely. 



The selection and calculation of results brought to view in 

 Table II. will show that, when experiments are conducted with 

 pigs fed on good fattening food for periods of not less than 

 eight or ten weeks, the amounts both of total increase and of 

 fat stored up are so great in proportion both to the original 

 weight of the animal and to the food consumed, that the data 

 so obtained may be safely relied upon as a means of estimating, 

 with sufficient accuracy for the purposes of the present discus- 

 sion, from what constituent or constituents of the food the fat 

 of the animals has been derived. 



Experiment 1 . — In this experiment two pigs of the same litter, 

 of equal weight, and, as far as could be judged, of similar charac- 

 ter, were selected. One was killed at once, and the amount of 

 total dry or solid matter, nitrogenous substance, fat, and mi- 

 neral matter, in its body, determined. The other was then fed 

 for a period of ten weeks on a good mixed food, containing, 

 however, a more than usually high proportion of nitrogenous 

 substance. It was then weighed and killed, and its composi- 

 tion was determined as in the case of the other animal. The 

 results so obtained supplied an important portion of the data 

 requisite for the calculation of the composition of the increase 

 in the other cases *. The food consisted of a mixture of beau- 

 meal, lentil-meal, , and bran, each one part, and barley-meal 

 three parts, given ad libitum. 



* For further details relating to this and the other experiments, ve 

 must refer to our former papers, as follow : — " On the Composition of 

 Foods in relation to Respiration and the Feeding- of Animals/' Report 

 of the British Association for the Advancement of Science for 1852. 

 " Agricultural Chemistry: Pig Feeding," Journ. Roy. Ag. Soc. Eng. 

 vol. xiv. part 2, 1853. " On the Equivalency of Starch and Sugar in 

 Food," Report of the British Association for 1854. a Experimental In- 

 quiry into the Composition of some of the Animals Fed and Slaughtered 

 as Human Food," Phil. Trans, part 2, 1859. 



