152 



cannot be said to assist in the formation of new tissue — muscle, blood, 

 &c., but are of service as fuel in developing the necessary heat and 

 energy. Of course, the fats they contain may be so used, or deposited 

 as such in the adipose tissues. 



Water and mineral matters are common to both classes of foods. 

 While both are absolutely necessary, they can scarcely be called nutrients. 

 Water is the universal solvent. Dependent ui)on its presence are the 

 processes of digestion and assimilation. The blood and lymph are 

 largely water, and by them the nutri ive matter is conveyed to every 

 part of the body. It also takes part in the elimination of waste 

 products. Mineral matters, especially common salt and phosphate 

 of lime are required tor tissues and bonis. "The salt m the blood 

 holds the albuminoids in solution, and by regulating the amount of water 

 in the blood corpuscles and the cellular elements of the tissues, preserves 

 their forrn and consistence." Phosphate of lime gives solidity to the 

 bones and teeth, and is also present in muscle, milk, &c. 



Composition and Digestibility of the More Common Foods. 



We may now consider the composition and digestibility of some of 

 the mote common foods. In the subjoined table, obtained from the 

 same source as the pieceding, the percentage indigestible, as well as the 

 total amount of each nutrient is given. It is a very instructive 

 chart and one that well deserves a careful study. It shows most clearly 

 the large amount of albuminoids, entirely digestible, in the animal foods 

 (meats and fish), and that in such, increased fat generally means 

 decreased water. This is exemplified in the case of fat pork. The carbo- 

 hydrates (starch and sugar) are practically absent in these foods. Eggs 

 we see to b^ a highly concentrated food, being rich in albuminoids and 

 fat, but containing no starch or sugar. Fish, generally speaking, is a 

 very nutritious food, being easy of digestion. Its value as a brain food 

 will be spoken of later on. Cod may be considered albuminoids and 

 water. Milk is shown to be a well balanced food — /. e. it contains all 

 the materials in good proportions and approaches most nearly the com- 

 position of a ' perfect food.' Its almost total digestibility makes it a 

 most important factor in the diet of the young and aged. It has been 

 found that boiling milk somewhat impairs its digestibility. Butter may 



