INCOME AND EXPENDITURE OF THE BODY. 301 



sition of the daily wastes of the living Body is tolerably con- 

 stant; it does not simply lose a quantity. of matter weighing 

 so much, but a certain amount of definite kinds of matter, 

 carbon, nitrogen, oxygen, and so on; and these same sub- 

 stances must be restored to it from outside, in order that life 

 may be continued. To give a stone to one asking for bread 

 might enable him, if he swallowed it, to make up the weight 

 of matter lost in twenty-four hours; but bread would be 

 needed to keep him alive. The Body not only requires a 

 supply of matter from outside, but a supply of certain definite 

 kinds of matter. 



The Losses of the Body in Energy. The daily expendi- 

 ture of matter by the living Body is not the only one: as 

 continuously it loses in some form or another energy, or the 

 power of doing work; often as mechanical work expended in 

 moving external objects, but even when at rest energy is con- 

 stantly being lost to the Body in the form of heat, by radia- 

 tion and conduction to surrounding objects, by the evaporation 

 of water from the lungs and skin, and by removal in warm 

 excretions. Unless the Body can make energy it must there- 

 fore receive a certain supply of it also from the exterior, or it 

 would very soon cease to carry on any of its vital work ; it 

 would be unable to move and woui/l cool down to the temper- 

 ature of surrounding objects. The discoveries of this century 

 having shown that energy is as inuestructible and uncreatable 

 (see Physics) as matter, we are led to look for the sources of 

 the supply of it to the Body; and finding that the living Body 

 daily receives it and dies when the supply is cut off, we no 

 longer suppose, with the older physiologists, that it works by 

 means of a mysterious vital force existing in or created by it; 

 but that getting energy from the outside it utilizes it for its 

 purposes for the performance of its nutritive and other living 

 work and then returns it to the exterior in what the physi- 

 cists know as a degraded state; that is, in a less utilizable 

 condition. While energy like matter is indestructible it is, 

 unlike matter, transmutable; iron is always iron and gold 

 always gold; neither can by any means which we possess be 

 converted into any other form of matter; and so the Body, 

 needing carbon, hydrogen, oxygen, and nitrogen to build it 

 and to cover its daily losses, must be supplied with those very 

 substances. As regards energy this is not the case. While 

 the total amount of it in the universe is constant, its form is 



