18 
POPULAR SCIENCE REVIEW. 
converting starcli into sugar. It is contained in many plants, 
especially in fruits ; but it is separated from the sugar-cane 
and other plants, and used by man in its pure state. It sup- 
plies carbon for the animal stove, and is justly regarded as a 
heat-giver. 
Starch and sugar are converted in the vegetable system into 
fat by the loss of their oxygen. Fat contains large quantities 
of carbon and hydrogen, and but little oxygen. The conse- 
quence is that when fat, in any form (whether what we call 
butter, lard, suet, or oil), is introduced into the system, it offers 
hydrogen as well as carbon for combination with oxygen. For 
the purposes of maintaining animal heat one pound of butter 
or oil goes as far as two pounds of sugar or two pounds and 
a half of starch. It frequently happens in the animal system 
that, when the carbon of the sugar and starch is not 
required for animal heat, they lose their oxygen and become 
converted into fat. In this way they are deposited in the 
system, and animals fed on an excess of starch and sugar 
become fat. In the summer season, when the animal system 
has less demand for heat, herbivorous animals become 
fat. Man himself becomes fat at this season by consuming 
the usual quantities of starch and sugar. This is a point of 
great practical importance to those who do not wish to become 
fat. It is not only necessary that they should not consume fat, 
but that they should not consume those substances which 
contain starch and sugar, and which, if taken in larger quanti- 
ties than suffice to maintain animal heat, are converted into fat. 
Fat and its analogues, butter, suet, and oil, are not only 
taken as a means of supporting animal heat, but are found 
essential to the development of some important tissues. 
Muscles and nerves cannot form without fat. Hence it is 
that in those states of disease where wasting of the 
tissues occurs, one of the best possible remedies is fat ; and 
so important is this, that the introduction of animal fat, in the 
shape of cod-hver oil, has been found one of the most im- 
portant remedies in all cases of wasting disease. 
On the other hand, there are deranged conditions of the 
system in which the sugar and fat are not oxidised, but are 
deposited in the form of adipose tissue in the system. This 
adipose matter either accumulates from this cause, or from the 
too free ingestion of sugar and fat. The remedy in the latter 
case is simply to stop the supplies ; the treatment in the former 
case demands more inquiry, and consists in the removal of 
any impediment which may exist to the free oxygenation of 
the carbonaceous materials. 
A second group of foods are those which, in addition to 
carbon, hydrogen, and oxygen, contain Nitrogen. The 
