792 The American Naturalist. [October, 
To produce 100 pounds increase the oxen consumed more 
dry substance of food than the sheep, and of coarse fodder 
there was twice as much hay requiring a larger expenditure 
of energy to dispose of it, and a smaller amount was utilized 
and stored in the increase which contained less dry substance. 
There was also a larger loss in the excreta and a greater ex- 
penditure in repairs of the system and other physiological 
processes, resulting from the increased metabolism. 
A comparison of tables 2 and 3 will show that less work is 
required to dispose of the smaller amount of coarse feed in the 
rations of the sheep, and with less dry substance of feed they 
give a much better proportionate return in increase than the 
oxen; while the pigs fed on barley meal alone make the same 
increase from less than one-half the dry substance of feed 
consumed by the sheep, with a diminished waste in excreta, 
and the repairs of the system and other physiological processes 
are carried on with a comparatively small expenditure of en- 
ergy. 
The fourth column of table 3 is, however, of special inter- 
est in relation to the processes of nutrition, and the difference 
in the results we have been discussing. One of the most 
marked results of proteid substances in the food, now recog- 
nized by physiologists, is to increase the metabolism of the 
system. From the small amount of proteid substance. stored 
up in the increase of fattening animals, as shown in tables 1 
and 3, an active metabolism of the system must be carried on 
to dispose of any considerable excess supplied in the food, as 
all that is digested and not retained in the increase is dis- 
charged by the kidneys in the form urea. The supply of en- 
ergy to carry on the increased metabolism of the system aris- 
ing from an excess of proteid food is, to some extent, however, 
immediately provided for in the heat liberated in its conver- 
sion into urea. 
The oxen, with 218 pounds of proteids in their feed, give 
the smallest return in increase, the largest amount of waste in 
excreta, and decidedly more work is required in repairs of the 
system and other physiological processes resulting from the 
increased metabolism. The pigs fed on barley meal, with only 
