SOME OF THE ANIMALS FED AND SLAIJGHTEEED AS HITMAN FOOD. 555 
on that of the nitrogenous ones. In fact, when we reflect upon what we already know 
of the relations of the constituents of the animal body to those taken into it as food- 
thanks more particularly to Mulder, to Boussingault, and to Liebig — and when we 
furthei consider the facts now adduced as to the Composition of Increase^ it would seem 
httle else than a truism to say, that as our fattening food-stufis go, their comparative 
values, as such*, are not determinable by their percentage of nitrogenous compounds. 
In the absence of sufiicient direct evidence, such as we have endeavoured to supply, as 
to the probable composition of the increase of animals feeding for the butcher, an oppo- 
site opmion has generally been maintained. A. consideration of the essentialness of the 
nitrogenous compounds of food, for the formation of the most important animal struc- 
tures, has doubtless had much to do with determining the view in question ; and it 
would seem, that keeping this point very prominently in view, it has been assumed, 
without the requisite experimental data, that these essential nitrogenous compounds 
were geneially relatively deflcient in our current foods. It would be more nearly true 
to say, that the digestible and assimilable wow-nitrogenous constituents are generally in 
defect relatively to the digestible and assimilable nitrogenous compounds in our foods. 
The comparative values of food-stufls are, however, not to be unconditionally deter- 
mined by their percentage of either of these equally important classes of constituents. 
It has, rt rs true, been frequently maintained, that a certain relation of the one class of 
constituents to the other, varying according to circumstances, is essential in a truly 
rational diet. But the practical bearings of the principle, seem to have been lost sight 
of by some of those who have the most prominently insisted upon it in its abstract form, 
as soon as they came to estimate, according to analysis, the comparative values of 
difierent foods. 
The lecords of the numerous ultimate analyses of foods which have been hitherto 
made, are nevertheless of high value and interest in a statistical point of view. But 
now possessing them, as the basis of certain general estimates, the next desideratum is 
to examine more closely into the nature and condition of the proximate compounds 
of food-stuffs— to distinguish those which are digestible and assimilable, from those 
which are not so— to determine the comparative values of the comparable or mutually 
replaceable portions (both intrinsically and according to the varying exigencies of the 
system)— and above all, to flx our standards of comparative value with more of reference 
to direct experimental evidence on the point, and to existing knowledge of the compo- 
sition of animal bodies, than has been hitherto usual or even possible. 
* As, however, the manure from highly nitrogenous foods is the most valuable, it frequently becomes, in 
this point of view, the interest of the farmer— provided the character be in other respects equal— to purchase 
and use those having the higher amounts of nitrogen. 
