INCOME AND EXPENDITURE OF BODY. 65 



numbers (in grains) in the two tables is of course diagrammatic. No such 

 exactitude in the account occurs in any living body, in the course of any 

 given twenty-four hours. But any difference which exists between the 

 two amounts of income and expenditure at any given period, corresponds 

 merely with the slight variations, in the amount of capital (weight of 

 body), to which the healthiest subject is liable. 



The chemical composition of the food (p. 213, Vol.1.) may be profitably 

 compared with that of the excreta, as before mentioned. The greater part 

 of our food is composed of matter, which contains much potential energy; 

 and in the chemical changes (combustion and other processes), to which 

 it is subject in the body, active energy is manifested. 



3. The Sources and Objects of Expenditure. The sources of 

 necessary waste and expenditure in the living body are various and ex- 

 tensive. They may be comprehended under the following heads: (1) 

 Common wear and tear; such as that to which all structures, living and 

 not living, are subjected by exposure and work; but which must be 

 especially large in the soft and easily decaying structures of an animal 

 body. 



(2) Manifestations of Force in the form either of Heat or Motion. In 

 the former case (Heat), the combustion must be sufficient to maintain 

 a temperature of about 100 F. (37 '8 C.) throughout the whole sub- 

 stance of the body, in all varieties of external temperature, notwithstand- 

 ing the large amount continually lost in the ways previously enumerated 

 (p. 313, Vol. I.). In the case of Motion, there is the expenditure involved , 

 in (a) Ordinary muscular movements, as in Prehension, Mastication, Lo- /y 

 comotion, and numberless other ways: (b) Various involuntary movements, 



as in Eespiration, Circulation, Digestion, etc. 



(3) Manifestation of Nerve-force; as in the general regulation of all 

 physiological processes, e.g., Eespiration, Circulation, Digestion; and in 

 Volition and all other manifestations of cerebral activity. 



(4) The energy expended in all physiological processes, e.g., Nutrition, 

 Secretion, Growth, and the like. 



The Total expenditure or manifestation of energy by an animal body 

 can be measured, with fair accuracy; the terms used being such as are 

 employed in connection with other than vital operations. All statements 

 however, must be considered for the present approximate only, and es- 

 pecially is this the case with respect to the comparative share of expendi- 

 ture to be assigned to the various objects just enumerated. 



The amount of energy daily manifested by the adult human body in 

 (a) the maintenance of its temperature; (b) in internal mechanical work, 

 as in the movements of the respiratory muscles, the heart, etc. ; and (c) in 

 external mechanical work, as in locomotion and all other voluntary move- 

 ments, ha^been reckoned at about 3,400 foot-tons (p. 124, Vol. I.). Of this 

 amount only one-tenth is directly expended in internal and external 

 VOL. II. 5. 



