of the Fat of the Animal Body. 449 



stance was in considerable excess over the amount and propor- 

 tion usually supplied — there was, according to the calculation, 

 more than sufficient carbon possibly available from the nitro- 

 genous substance of the food for the formation of the fat esti- 

 mated to be produced. 



In Exps. 4 & 5, however, in which the relation of the non- 

 nitrogenous to the nitrogenous substance in the food was much 

 more nearly that in the usual food of the well-fed fattening pig, 

 it is reckoned that there was about 40 per cent, of the carbon 

 of the produced fat which could not possibly have been supplied 

 from the nitrogenous constituents of the food. 



In the other experiments (Nos. 6, 7, 8 & 9), in which 

 again the proportion of the non-nitrogenous to the nitrogenous 

 constituents of the food was lower than usual (though not so 

 much so as in Exps. 1, 2 & 3) — in which, in fact, the nitro- 

 genous constituents were in excess — there was still a consider- 

 able proportion of the carbon of the produced fat which the 

 nitrogenous constituents of the food could not possibly have 

 supplied. 



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

 mode of illustration we have adopted, the figures show not only 

 the utmost proportion of the carbon of the stored-up fat which 

 could possibly have had its source in the nitrogenous substance 

 of the food, but even notably more than could possibly have 

 been so derived. Thus, to say nothing of other considerations, 

 it has been assumed for simplicity of illustration, and granted 

 for the sake of argument, that the whole of the ready-formed 

 fatty matter of the food contributed to the fat stored up, that 

 the whole of the nitrogenous substance of the food not stored up 

 as increase would be perfectly digested and become available for 

 the purposes of the system, 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. It is ob- 

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

 and in part quite inadmissible, and that the tendency of each 

 of them is to show too large a proportion of the produced fat 

 to have been possibly derived from the nitrogenous constituents 

 of the food. 



The amount of fat necessarily derived from other sources 

 than the nitrogenous constituents of the food must therefore 

 be greater than our mode of estimate can indicate ; and it is 

 obvious, from the figures given in the Table, that the less the 

 excess of nitrogenous substance in the food, the greater was 

 the proportion of produced fat which must necessarily have had 

 its source in the carbo-hydrates of the food, and that, at any rate 

 in those cases in which the proportion of non-nitrogenous to 



Phil. Mag. S. 4. Vol. 32. No. 218. Dec. 1866. ^2 G- 



