THE GENERAL NATURE OF DIET 151 



relatively tasteless, while the salts and savory extractives pass largely 

 into the water. Prolonged boiling may redissolve some of the coagulated 

 proteids. In boiling, unless under pressure, the temperature does not 

 exceed 100 C. Boiling is chiefly important as a means of cooking vege- 

 tables, for it makes starchy foods available as food which raw would be 

 quite indigestible and even irritating to the gut. In the processes of 

 roasting and broiling, essentially alike in action, the material should be at 

 first subjected to a high degree of heat, 200 or higher. This coagulates 

 the outside of the mass into a sort of shell, which retains, more or less 

 unchanged, the juices and, in case of meat, the salts, extractives, and 

 soluble albumins. Flesh which has been heated not above 70 is the 

 most digestible, for even this degree of heat changes the connective- 

 tissue which binds the muscle-bundles together to gelatin and renders 

 the meat more easily masticated. The high heat of the first part of 

 roasting also develops in the fats of the meat several very savory fatty 

 acids, and thus provides useful flavors not otherwise obtained. In 

 frying, the heat is conveyed to the interior of the food by means of melted 

 fat of various sorts, commonly lard, butter, or suet. This provides a 

 very high degree of heat which more or less penetrates the mass and 

 produces effects somewhat like those of prolonged and excessive baking 

 or roasting. The fat, however, tends to surround with a film each par- 

 ticle of the meat or vegetable, and so renders it relatively indigestible. 

 The excessive use of fried food, caused by its relative ease and cheapness, 

 is one of the curses of American habits of cooking, it being often used 

 when broiling would be very much better for the consumer. Preserving 

 is a mode of preparing food so that it will keep indefinitely. It consists 

 usually of some process of sterilizing (commonly by heat), the material 

 being then sealed from the putrefactive germs of the air. In jellies the 

 sugar acts as a preservative. Almost every sort of meat, vegetable, and 

 fruit is now thus prepared in glass or in tin, and so made for indefinite 

 periods of time available in any part of the world. In some cases the use 

 of artificial preservative substances renders the foods so prepared difficult 

 of digestion, but most of the objections made on this score seem 

 unfounded. The elaborate test-experiments made by the United States 

 Government chemists tended to the principle that while boric acid, for 

 example, would probably irritate a digestive apparatus unduly if taken 

 in considerable quantities continuously, in the amount apt to be ingested 

 by the average person on an average diet practically no harm would 

 ensue. The cold-storage problem (fowls, for example, often being kept, 

 it is said, two years or more) is in practice a more important question. 

 However low the temperature, in time protoplasm probably undergoes 

 degeneration, which makes it more. and more unsuitable for human food. 

 The smoking of flesh-meats, including fish, and the drying of meats, 

 vegetables, and fruits is a valuable mode of preserving food for a shorter 

 period than in case of hermetical sealing from the air. Nutrients so 

 prepared are liable to be infested by worms and by mould, and, in many 

 cases, at least, are relatively lacking in flavor, except that of salt or of the 



