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food, are made up of different constituents. These we may 

 classify as follows : 



I. Edible substance, e. g:, the flesh of meats and fish, the 

 shell contents of oysters, wheat flour. 2. Refuse, e.g., bones 

 of meat and fish, the shells of oysters, bran of wheat 



The edible substance consists of: i. Water. 2. Nutritive 

 substance or nutrients. Leaving out of account the refuse and 

 the water, we may consider simply the nutriments. Speaking 

 as chemists and physiologists, we may say that our food sup- 

 plies, besides mineral substances and water, three principal 

 classes of nutritive ingredients, viz. : Protein, carbohydrates, 

 and fats ; and that these are transformed into the tissues and 

 fluids of the body, muscle and fat, blood and bone, and are con- 

 sumed to produce heat and force. 



The principal nutrient of fish is protein. In chemical com- 

 position the protein offish is essentially the same as that which 

 makes up the bulk of the nutritive material of very lean meat. 

 In both lean meat and in fish it is called myosin. It is very 

 similar to the albumen (white) of egg, the casein (curd) of milk 

 and the gluten of wheat. The protein compounds are some- 

 times called " flesh formers." They are the most important of 

 the nutritive ingredients of food, because they are the only ones 

 that contain nitrogen and they alone make muscle, tendon and 

 other nitrogenous tissues of the body. Of the fats we have 

 familiar examples in the fat of meat and fish, lard, butter, olive 

 oil and other kinds of oil, including the oil of corn and wheat. 

 Some kinds offish, as salmon, shad and mackerel contain con- 

 siderable fat, but the flesh of codfish, haddock, pike, perch, bass, 

 bluefish and the most of our common food fishes contain very 

 little fat, less, indeed, than is found in even the leanest meat. 

 Of the carbohydrates, sugar and starch are the most import- 

 ant. The carbohydrates make the chief nutritive material of 

 vegetable foods. Oysters and clams contain a certain amount 

 of carbohydrates, as does milk. These different substances in 

 food have different kinds of work to do in nourishing the body. 

 The protein compounds, which are the only ones that contain 

 nitrogen, make the muscle, tendon and other nitrogenous 

 tissues. This, the carbohydrates and fats, which contain no 



