SOME OF THE ANIMALS FED AND SLAHQ-HTEEED AS HUMAN FOOD. 551 
Both practical and chemical considerations seem to indicate that Fat may be produced 
in the animal body, by the transformation within it of nitrogenous compounds. But it 
seems probable, that at least the main source of the produced Fat will be the wow- 
nitrogenous constituents of the food. Of these, particularly in the fattening food of 
Pigs, the most prominent item is starch. It seemed desirable, therefore, to adopt this 
substance as the basis of the illustration of the probable amount of the constituents 
involved in the formation of the produced Fat, in the experiments in question. 
The question arises, how much Starch will be requmed for the production of a given 
amount of Fat 1 At present but little is known as to the relative proportions in which 
the different Fats exist in different animals. Nor are chemists agreed as to the formulee 
to be gi\en to the several natural animal Fats. It would only be a doubtful refinement, 
therefore, to adopt for our purpose the exact rational formula given for any one of the 
more important fatty bodies, and from it to calculate, in equivalents, the amount of Starch 
required to produce an equivalent of the Fat, and also the number of equivalents of the 
collateral products. It is better to adopt an average percentage composition merely ; 
and for want of more exact data, we take the mean of the three most important animal 
fats — namely, tri-stearine, tri-margarine, and tri-oleine. This gives, in round numbers, 
/7 per cent, of carbon, 12 per cent, of hydrogen, and 11 per cent, of oxygen for the 
crude mixed fats. It may be mentioned, however, that tri-oleine is stated to be in 
laiger proportion to the other fats in Pigs, than in either Sheep or Oxen. Assuming 
the oxygen which is eliminated in the formation of Fat from Starch, to go off with a 
portion of its hydrogen in the form of water, and the remainder with carbon in the form 
of carbonic acid, it would require as a minimum, 2-45 parts by weight of Starch to con- 
tribute to the formation of one part by weight of the mixed Fats -f- the collaterally 
formed water and carbonic acid. If the stearine predominated, this mode of calculation 
would show the amount of Starch required to be rather higher, and if the oleine, rather 
lower than 2-45 for 1 of the Fat. As the above number is the lowest amount of Starch 
which would, in the manner supposed, yield 1 part of the mixed Fats of the percentage 
composition above assumed, we may adopt the convenient round number 2-5 as the 
amount of Starch probably on the average required for the formation of 1 part of the 
mixed Fats of the body, when these have their source in that substance. This number 
then (2-5), is that by which we multiply, for the purposes of the Table, the amount of 
the estimated Fat m the increase of the Pigs, over and above the ready formed fojt they 
consumed in them food, to ascertain the amount of the dry substance in the food (if in 
the form of starch), required for the production of that amount of Fat which could not 
have been directly derived from the food as such, and must therefore have heen formed 
within the body of the animal. Whilst adopting the mode of calculation here described, 
as usefully, and sufficiently closely, illustrating the point in question, it may be remarked 
m passing, that when Fat is formed from the nitrogenous compounds in the body, a less 
amount of dry substance of the food would then be required for the formation of a given 
amount of Fat, than when it is produced from Starch. On the other hand, if Sugar were 
4 c 2 
