•i38 On the Composition of Oxen, Sheep, and Pi()s, 
amounts are, liowpver, much less than the actual figures show, 
Avhen due allowance is made, both for those of the non-nitrogenous 
constituents of the food which would probably be indigesti- 
ble and pass through the animal unchanged, and also for the 
different respiratory and fat-forming capacities of the portions 
Avhich are digestible and available for the purposes of the animal 
economy. 
It must further be remembered that, even if all due allow- 
ance, such as is here supposed, were made, the amounts must 
still cover all variations — whether arising from differences in 
the external conditions of the experiments, from individual pecu- 
liarities in the animals themselves, from the different amounts 
stored up according to the suitableness of the foods, as well as 
from the many other uncontrollable circumstances which must 
always interfere with any attempts to bring within the range of 
accurate numerical measurement, the results of those processes 
in whi( h the subtle principle of animal life exerts its inHuence. 
On the other hand, with a general uniformity in the amounts 
of available now-nitrogenous constituents consumed (by a given 
weight of animal within a given time, and to produce a given 
amount of increase), those of the nitror/cnous constituents are 
found to vary, under the same circumstances, in the proportion 
of from 1 to 2 or 3. Nor (excepting in a few cases) can this 
great variation be attributed to difference in the condition of the 
nitrogenous substances in regard to digestibility and assimila- 
bililv. 
The pig requires much less of mere hulk in his food than either 
the ox or the sheep. Whilst the fattening food of the latter 
animals is principally composed of grass, or hay or straw, and 
roots, with a comparatively small proportion of cake or corn, that 
of the pig comprises a larger proportion of corn, and its dry 
substance consists, weight for weight, of a much larger proportion 
of digestible or convertible constituents (starch, sugar, &c., and 
highly-elaborated nitrogenous compounds), and contains much 
less of effete .woody-fibre, than does that of oxen and sheep. 
Notwithstanding the generally richer character of his food, the 
fattening pig is found to consume a much larger quantity of dry 
substance in relation to his weight than the sheep. He at the 
same time yields a larger amount of increase in proportion to the 
dry substance of the food consumed. 
For practical purposes it may be assumed, that sheep, when 
fed liberally upon good fattening food composed of a moderate 
proportion of cake or corn, a little hay or straw chaff, together 
with roots or other succulent food, will yield, over *a con- 
siderable period of time, 1 part of increase in live-weight for 
from 8 to 10 parts of the dry substance of such mixed food. The 
