Food and its Digestion. 



247 



Those substances which are characterized by the pre- 

 sence of nitrogen, such as albumen, musculin, casein, gluten 

 and others, are principally of use in forming tissue, though 

 they also aid in sustaining the heat of the body. 



The fats, composed of carbon, hydrogen and oxygen — 

 sometimes called hydro-carbons, are preeminently heat pro- 

 ducers, and yet they are essential to the formation of tissue. 



The amylaceous, or starchy and saccharine groups, also 

 called carbo-hydrates, are mainly useful for the produc- 

 tion of heat, though they likewise enter into the compo- 

 sition of some of the tissues. Now to these we must add 

 such inorganic substances as water, and certain minerals. 



The demand for food is always regulated by the waste 

 of the tissues, hence the process of growth requires constant 

 supply, and this too, is increased or diminished by the 

 condition of the respiration and the amount of bodily or 

 mental exertion, all of which circumstances induce a loss 

 of force and likewise of texture. 



In endeavoring to ascertain what may be the best kinds 

 of food requisite for meeting these demands, the following 

 circumstances must be regarded: 



First. The chemical principles which enter into the 

 composition of the living being which is to be nourished. 



Second. The mode in which these are combined to form 

 tissues and organs. 



Third. The atmosphere surrounding the living being. 



Fourth. The amount of waste produced as among men 

 variously employed. 



The chemical principles are the albuminous, the fatty, 

 saccharine and mineral, and of all articles of food milk appears 

 to be that one which contains these essential substances 

 in the best proportion. No one of these groups of prin- 

 ciples alone will serve to keep up nutrition in an animal 

 body, they must be united as milk illustrates. Its casein 

 being the albuminoid principle, its cream being the olea- 

 ginous, and the sugar of milk the saccharine, together 

 with the mineral principles which are held in solution. 



