16 
POPULAE SCIENCE EEVIEW. 
to form thirty-five ounces of carbonic acid^ and this is the 
source of the diminished weight of a human body when no 
food is taken. 
In addition to this, I calculate that there passes from the 
body one hundred and three ounces of water ; fifty-one by the 
kidneys, thirty-one by the lungs, sixteen by the skin, and five 
by the alimentary canal. In addition to the water, there are 
dissolved in it two ounces and a half of soluble salts, including 
urea (a substance containing nitrogen), and about two 
ounces of insoluble matter. In all, a body weighing one hun- 
dred and fifty-four pounds loses every day about one hundred 
and forty-three ounces. 
In living, moving, and acting, then, the human body loses 
about a sixteenth of its own weight every day. The supply 
for all this waste is food. The necessity for food is this waste. 
If we examine the composition of food we shall find that it 
has in it the same compounds and the same elements as we 
find in the human body. If we place all the variety of foods 
which man consumes, from his first meal in the morning to the 
last at night, under chemical analysis, we shall find that they 
only contain the elements of his body. Nay, four of these 
are so prominent above all the rest that recent writers on 
dietetics confine their attention principally to these four, 
namely, — carbon, hydrogen, oxygen, and nitrogen. In a body 
weighing one hundred and fifty-four pounds, they form one 
hundred and forty-nine pounds and a half. 
We now begin to see how science is teaching man the 
difference between bad and good food. That food alone is 
good which has a proper quantity of each of the elements of 
which the body is composed. It must not, however, be sup- 
posed that the immediate destination of the food is to be 
carried into the blood, and there to undergo the changes which 
result in the waste to which we have referred. No ; the food 
is first taken into the stomach, and there undergoes physical 
and chemical changes which fit it to become blood. The 
blood supplies all the organs with the new matter, and receives 
from them the old, effete, or used matter, which is the portion of 
the body that becomes waste and passes from it. The body is 
thus hourly, nay constantly, being built up and taken down. 
The physical and chemical forces, acting on particles of matter 
too minute for even microscopic vision, are perpetually per- 
forming this great work, and the grand result of this perpetual 
activity is life. It is thus that the body in which we live is 
perpetually passing away. It changes from hour to hour and 
from day to day. Some portions of the body pass rapidly 
away, as the muscles, nerves, and soft parts generally; whilst 
others, as the skin, the nails, the hair, and the bones, more 
