and of their Incivase whilst Fc'ittcning. 
435 
The so-callod nifroqenoits substance, calculated from the amount 
of nitrogen the food contains, must obviously be of very different 
character, according to the description of the food. In ripened 
products it will probably be available for the purposes of the system 
in larger proportion than in iinripened or succulent ones. In 
unripencd vegetable products a considerable portion of the nitrogen 
often exists in a condition in which, if not injurious, it is, to say 
the least, certainly not assimilable. Even in ripened ones it may 
exist in very different degrees of digestibility and assimilability. 
Again, the so-called " nor<-nitrogenous substance" may include 
cellulose (or " woody-fibre"), starch, sugar, or gum — all of which 
have a very similar chemical composition ; also various bodies of 
the pectine class ; and fatty matter. 
Recent investigations have demonstrated that a considerable 
proportion of the more delicate cellulose of our current food-stuffs, 
may be digested ; and so far as it is so, its value as a constituent 
of food will probably range pretty closely with that of sugar and 
of starch. But, a large proportion of the woody-fibre, included 
under our term 7<o?Miitrogenous substance, is passed by the animal 
entirely undigested. 
So far as can be judged, the pectine compounds have, weight for 
weight, a somewhat less feeding value than either starch or sugar. 
Lastly, for practical purposes, a given amount of fatty matter 
in food, may be considered as equivalent to about 2^ times its 
weight of starch, or sugar. 
From the above considerations it will be obvious that, in 
reading the actual figures given in the Tables, regard must be 
had to the known character (according to the description of the 
foods employed) of the substances classed respectively as " nitro- 
genous," and " non-nitrogenous." In our fuller Reports, already 
referred to, we have called attention to this point ; and so far as 
the experiments with pigs ai'e concerned, the food of which 
contains comparatively little indigestible woody-fibre, we have so 
far distinguished between the different non-nitrogenous constituents, 
as to give the fatty matter, and the non-nitrogenous substance not 
fat, separately. 
With these explanatory observations we proceed, very briefly, 
to call attention to the more general conclusions to be drawn from 
the results. 
It is seen that, in all cases comparable on the point, there is 
much more of uniformity of amount within the columns of non- 
nitrogenous substance, and total dry substance, than in those of 
the nitrogenous substance. This is the case both in regard to the 
quantities consumed — to a given xceight of animal within a given 
time, and to those consumed — to produce a given amount of increase 
in live-weight. The deviations from the general regularity in the 
amounts. 
