INTRODUCTION. 3 
together with more or less mineral matter, are separated by the 
organism, in the processes of digestion and resorption, from the un- 
essential or unavailable matters of the food. The latter are rejected 
from the body, while the former are used by it to take the place 
of the material broken down and excreted by its vital activities, 
and thus serve to maintain its capital of matter and of potential 
energy. 
In other words, the food may be regarded as the vehicle by 
means of which a little portion of the “infinite and eternal energy 
from which all things proceed ” is put for the time being at the 
service of the individual ; as being not so much a supply of matter 
to make good the waste of tissue as a supply of energy for the mani- 
festations of life. 
The animal body, then, from our present standpoint, consists of 
a certain amount of matter which has been temporarily segregated 
from the rest of the universe and which represents a certain store 
or capital of potential energy. This aggregate of matter and 
energy is in a constant state of change or flux. On the one hand, 
its vital activities are continually drawing upon its capital. By 
the very act of living it expends matter and energy. On the other 
hand, by means of the function of nutrition, it is continually receiv- 
ing supplies of matter and energy from its environment and adding 
them to its capital. Plainly, then, the growth, the maintenance, or 
the decay of the bedy depends upon the relation which it is able to 
maintain between the income and the expenditure of matter and 
energy. If the two are equal], the animal is simply maintained 
without increase or decrease; if the income is greater than the 
expenditure, the body adds to its capital of matter and energy, if 
the income is less than the expenditure, the necessary result is a 
diminution in the accumulated capital which, if continued, must 
ultimately result in death. 
We thus reach an essentially statistical standpoint, and this’ 
aspect of the subject of nutrition, which has been designated by 
some writers as “The Statistics of Nutrition,” forms the subject of 
the succeeding pages. The topic naturally divides itself into two 
distinct although closely related parts, viz.: 
1. The income and expenditure of matter. 
2. The income and expenditure of energy. 
