344 PRINCIPLES OF ANIMAL NUTRITION. 
so far as it is not removed from the body in the potential form in 
the secretions or excretions, ultimately takes the form of heat. 
Moreover, the fundamental features of glandular metabolism 
appear to be indentical with those of muscular metabolism. Thus 
Henderson * has shown that the active submaxillary gland of the 
dog does not lose nitrogen as compared with the inactive gland, 
but does lose weight, evidently from the metabolism of non- 
nitrogenous matter. Similarly, Bancroft t found the respiratory 
exchange of the same gland during activity to be three or four times 
that during rest. If we may accept these results as typical, we 
must conclude that glandular, like muscular metabolism is largely 
at the expense of non-nitrogenous matter, and shall not hesitate to 
summarize the two together as parts of the internal work of the 
body. 
CELLULAR Worx.—While both muscular and glandular work 
are forms of cell activity, a passing mention may be made for the 
sake of completeness of such processes as imbibition, filtration, 
osmosis, protoplasmic motion, karyokinesis, etc., which, while 
taking place in the various organs, are so general in their nature and 
form so essential a part of our conception of cell life that it seems 
proper to speak of them collectively as cellular work. As to the 
quantitative importance of these activities, so far as they can be 
differentiated from the special functions of the various organs, we 
lack the data for forming any definite conception, although it 
would appear that it must be small. 
Heat Production. 
As we have just seen, the forms of internal work are numerous 
and some of them are not readily accessible to measurement. All 
of them, however, have this in common, that the energy used in 
their performance ultimately assumes the form of heat. . 
This being the case, while the single factors making up the 
internal work are not readily determined, a determination of the 
total heat produced by a fasting animal in a state of rest (either 
directly or by computation from the amount and kind-of matter 
metabolized) will show the total amount of energy consumed in the 
* Am. Jour. Physiol., 8, 19. ft Journal of Physiol , 27, 31. 
