ANIMAL CHEMISTRY. 



freely in the air, or compelled to draw heavy 

 ourdens, the fat again disappears. 



It is evident, therefore, that the formation 

 of fat in the animal body is the result of a 

 f want of due proportion between the food 

 / taken into the stomach and the oxygen ab- 

 sorbed by the lungs and the skin. 



A pig, when fed with highly nitrogenized 

 food, becomes full of flesh; when fed with 

 potatoes (starch) it acquires little flesh, but 

 a ihick layer of fat. The milk of a cow, 

 when stall-fed, is very rich in butter, but in 

 the meadow is found to contain more ca- 

 seine, and in the same proportion less butter 

 and sugar of milk. In the human female, 

 beer, and farinaceous diet increase the pro- 

 portion of butter in the milk; an animal diet 

 yields less milk, but it is richer in caseine. 



If we reflect, that in the entire class of 

 carnivora, the food of which contains no 

 substance devoid of nitrogen except fat, the 

 production of fat in the body is utterly in- 

 significant; that even in these animals, as 

 in dogs and cats, it increases as soon as they 

 live on a mixed diet; and that we can in- 

 crease the formation of fat in other domes- 

 tic animals at pleasure, but only by means 

 of food containing no nitrogen ; we can 

 hardly entertain a doubt that such food, in 

 its various forms of starch, sugar, &c., is 

 closely connected with the production of fat. 



In the natural course of scientific research, 

 w- draw conclusions from the food in re- 

 ;<rd to the tissues or substances formed 

 from it; from the nitrogenized constituents 

 of plants we draw certain inferences as to 

 the nitrogenized constituents of the blood; 

 and it is quite in accordance with this, the 

 natural method, that we should seek to es- 

 tablish the relations of tho^e parts of our 

 food which are devoid of nitrogen and those 

 parts of the body which contain none of 

 that element. It is impossible to over- 

 look the very intimate connexion between 

 them. 



If we compare the composition of sugar 

 of milk, of starch, and of the other varieties 

 of sugar, with that of mutton and beef suet 

 and of human fat, we find that in all of 

 them the proportion of carbon to hydrogen 

 is the same, and that they only differ in that 

 of oxygen. 



According to the analyses of Chevreul, 

 mutton fat, human fat, and hogs' lard, con- 

 tain 29 percent, of carbon to 11.1, 11.4, 

 and 11.7 per cent, of hydrogen respec- 

 tively. (16) 



Starch contains 44.91 carbon to 6.11 

 hydrogen. 



Gutn and sugar 42.58 carbon to 6.37 

 hydrogen. (17) 



It is obvious that these numbers, repre- 

 senting the relative proportions of carbon 

 and hydrogen in starch, gum, and sugar, 

 are in the same ratio as the carbon and hy- 

 drogen in the different kinds of fat; for 

 44-91 : 6-11 =79 : 10-99 

 42-58 : 6-37 = 79 : 11-80 



From which it follows, that sugar, starch 

 and gum, by the mere separation of a part 

 of their oxygen, may pass into fat, or at 

 least into a substance having exactly the 

 composition of fat. If from the formula 

 of starch, C 12 H 10 O 10 , we take 9 equivalents 

 of oxygen, there will remain in 100 parts 



C 12 - - - 79-4 

 H 10 - - - 10-8 

 O - - - 9-8 



The empirical formula of fat which comes 

 nearest to this is C"H 10 O, which gives in 

 100 parts 



C - - - 78-9 

 H"> - - . 11-6 

 O - - 9-5 



According to this formula, an equivalent 

 of starch, in order to be changed into fat 

 would lose 1 equivalent of carbonic acid, 

 CO 2 , and 7 equivalents of oxygen. 



Now the composition of all saponifiable 

 fatty bodies agrees very closely with one or 

 other of these two formulae. 



If from 3 equivalents of sugar of milk, 



equivalents of water and 31 of oxygen, there 

 will remain C^H^O, a formula which ac- 

 curately represents the composition of cho 

 esterine, the fat of bile. (18.) 



Whatever views we may entertain re- 

 garding the origin of the fatty constituents 

 of the body, this much at least is undeni- 

 able, that the herbs and roots consumed by 

 "he cow contain no butter; that in hay or 

 :he other fodder of oxen no beef suet exists ; 

 hat no hogs' lard can be found in the po- 

 :ato refuse given to swine; and that the food 

 of geese or fowls contains no goose fat or 

 capon fat. The masses of fat found in the 

 bodies of these animals are formed in their 

 organism; and when the full value of this 

 act is recognised, it entitles us to conclude 

 hat a certain quantity of oxygen, in some 

 orm or other, separates from the constitu- 

 ents of their food; for without such a sepa- 

 ration of oxygen, no fat could possibly be 

 ormed from any one of these substances. 



The chemical analysis of the constituents 

 of the food of the gra'minivora shows in the 

 clearest manner that they contain carbon 

 and oxygen in certain proportions ; which, 



en reduced to equivalents, yield the fol- 

 owing series : 



n vegetable fibrine, albumen, and caseine, 



there are contained, for 



1 20 eq. carbon, 36 eq. oxygen. 

 n starch 120 100 



n cane sugar 120 110 



ngum 120 110 



n sugar of milk 120 120 



n grape sugar 120 140 



Now in all fatty bodies there are contained, 

 on an average 



For - 120 eq. carb. only 10 eq. oxygen. 



Since the carbon of the fatty constituents 

 of the animal body is derived from the food 



