OF FOOD. Ill 



albuminoid substances were known as the nutritious or " plastic" 

 elements. 



This distinction, however, has no real foundation. In the first 

 place, it is not at all certain that the sugars and the oils which dis- 

 appear in the body are destroyed by combustion. This is merely 

 an inference which has been made without any direct proof. All 

 we know positively in regard to the matter is that these substances 

 soon become so altered in the blood that they can no longer be 

 recognized by their ordinary chemical properties ; but we are still 

 ignorant of the exact nature of the transformations which they 

 undergo. Furthermore, the difference between the sugars and the 

 oils on the one hand, and the albuminoid substances on the other, 

 so far as regards their decomposition and disappearance in the 

 body, is only a difference in time. The albuminoid substances 

 become transformed more slowly, the sugars and the oils more 

 rapidly. Even if it should be ascertained hereafter that the sugars 

 and the oils really do not unite at all with the solid tissues, but are 

 entirely decomposed in the blood, this would not make them any 

 less important as alimentary substances, since the blood is as 

 essential a part of the body as the solid tissues, and its nutrition 

 must be provided for equally with theirs. 



It is evident, therefore, that no single proximate principle, nor 

 even any one class of them alone, can be sufficient for the nutrition 

 of the body; but that the food, to be nourishing, must contain 

 substances belonging to all the different groups of proximate prin- 

 ciples. The albuminoid substances are first in importance because 

 they constitute the largest part of the entire mass of the body ; and 

 exhaustion therefore follows more rapidly when they are withheld 

 than when the animal is deprived of other kinds of alimentary 

 matter. But starchy and oleaginous substances are also requisite ; 

 and the body feels the want of them sooner or later, though it may 

 be plentifully supplied with albumen and fibrin. Finally, the in- 

 organic saline matters, though in smaller quantity, are also neces- 

 sary to the continuous maintenance of life. In order that the 

 animal tissues and fluids remain in a healthy condition and take 

 their proper part in the functions of life, they must be supplied 

 with all the ingredients necessary to their constitution ; and a man 

 may be starved to death at last by depriving him of chloride of 

 sodium or phosphate of lime just as surely, though not so rapidly, 

 as if he were deprived of albumen or oil. 



In the different kinds of food, accordingly, which have been 



