184 ALIMENTATION. 



feel, a neutral reaction, and is insoluble in water and soluble in alcohol (particularly hot 

 alcohol), chloroform, ether, benzine, and solutions of soaps. The solid varieties are exceed- 

 ingly soluble in the oils. Treated with alkalies, at a high temperature and in the presence 

 of water, the fats are decomposed into fatty acids and glycerine, the acid uniting with the 

 base to form a soap. Alkaline, mucilaginous, and some animal fluids (particularly the 

 pancreatic juice) are capable of holding fat in a state of minute and permanent subdivision 

 and suspension, forming what are known as emulsions. 



The composition of many of the fats and oils has never been definitely ascertained, on 

 account of the difficulty in obtaining them in a state of absolute purity. They contain 

 carbon, hydrogen, and oxygen, but the latter elements do not exist in the proportions to 

 form water. 



As alimentary principles, fats and oils are undoubtedly of great importance. They 

 are supposed by many to be particularly concerned in the function of calorification. It 

 has been proven by repeated experiments that fat, as a single article of diet, is insufficient 

 for the purposes of nutrition. 



Inorganic Alimentary Principles, 



Physiological chemistry has shown that all the organs, tissues, and fluids of the 

 body contain inorganic matter in greater or less abundance. The same is true of vege- 

 table products. All the organic nitrogenized principles contain mineral substances which 

 cannot be removed without incineration and which must be considered as actually part 

 of their substance. When new organic matter is appropriated by the tissues to supply 

 the place of that which has become effete, the mineral substances are deposited with 

 them ; and the organic principles, as they become effete or are transformed into excre- 

 mentitious substances and discharged from the body, are always thrown off in connection 

 with the mineral substances which enter into their composition. This constant dis- 

 charge of inorganic principles, forming, as they do, an essential part of the organism, 

 necessitates their introduction with the food, in order to maintain the normal constitu- 

 tion of the parts. As these principles are as necessary to the proper constitution of the 

 body as any other, they must be considered as belonging to the class of alimentary sub- 

 stances. 



Water. This is one of the most important of the proximate principles of the organ- 

 ism, is found in every tissue and part without exception, is introduced with all kinds 

 of food, and is the basis of all drinks. As a rule, it is taken in greater or less quantity 

 in a nearly pure state. Although, as a drink, water should be colorless, odorless, and 

 nearly tasteless, it always contains more or less saline and other matters in solution, 

 with a certain quantity of air. The air and gases may be evolved by boiling or removing 

 the atmospheric pressure. Pure water does not exist in Nature. Even rain-water always 

 contains salts and frequently a little ammonia and organic matter. The waters of the 

 mineral springs, which are so abundant in parts of this country, are very rich in saline 

 constituents and generally contain a notable quantity of carbonic acid ; but the consid- 

 eration of their properties does not belong to physiology. The demand on the part of 

 the system for water is regulated, to a certain extent, by the quantity discharged from 

 the organism, and this is subject to great variations. The quantity taken as drink also 

 depends very much on the constitution of the food as regards the water which enters into 

 its composition. 



Chloride of Sodium. Of all saline substances, chloride of sodium is the one most 

 widely distributed in the animal and the vegetable kingdom. It exists in all varieties of 

 food ; but the quantity which is taken in combination with other principles is usually 

 insufficient for the purposes of the economy, and common salt is generally added to cer- 

 tain articles of food as a condiment, when it improves their flavor, promotes the seere- 



