326 FOOD AND DIGESTION 



chiefly potassium. Sodium chloride is an essential food; it is contained in 

 nearly all solid foods, but so much is required that it has also to be taken as a 

 condiment. Potassium salts are found in muscle, nerve, and in meats 

 generally, and in potatoes and other vegetables. Calcium salts are contained 

 in eggs, blood of meat, wheat, and vegetables. Iron is contained in hemo- 

 globin, in milk, eggs, and vegetables. 



Liquid Foods. Water is essential to life, and from two to two and a 

 half pints a day must be consumed in addition to that taken mixed with solid 

 food. Of the non-alcoholic substances which may be added to it for flavoring 

 purposes, such as tea, coffee, cocoa, etc., the last can alone be considered to 

 have a certain food value, as it contains fats, albuminous material, and starch, 

 the other constituents of such substances being a volatile oil, an alkaloid 

 caffeine, and tannic acid. The food value of alcoholic beverages, which has 

 long been a subject of controversy, as now generally agreed is but slight. 

 Beer, wines, and spirits contain ethyl alcohol, the amount varying from i . 5 

 to 4 . 5 per cent, in beer to 40 to 80 per cent, in spirits. 



The Effect of Cooking on Foods. In general terms cooking may 

 be said to render food more easily digestible, both directly and indirectly, 

 through increased palatability. Subjecting food to high degrees of heat also 

 serves to kill parasites, such as trichinae and the various tapeworms, which 

 may be present and alive in raw meats. In the case of meats various methods 

 of cooking are employed. In roasting, the meat in bulk is subjected to a 

 high temperature in an oven for a short time, 250 C. for 15 minutes, followed 

 by a somewhat lower temperature, 175 C., until the cooking is completed. 

 This causes a coagulation of the outer layers of albumin so that the juices 

 of the meat are retained. In boiling, the meat is first immersed in boiling 

 water for a time and then the cooking continues at a lower temperature. 

 In a broth, the extractives may be obtained by heating the meat in water for 

 a long period. Such a broth contains the flavoring and the stimulating 

 extracts of the meat, but is of only slight nutritive value. A temperature 

 below the coagulation point, at 60 C., will extract more nutritive protein 

 substance. For small pieces of meat, broiling practically serves the same 

 purpose as does roasting for larger pieces. Frying, as usually employed, 

 is the least serviceable method of preparation, since the fat of other oily 

 material used so permeates the food as to render it difficult of penetration 

 by the digestive juices. 



Cooking produces upon vegetables the necessary effect of rendering them 

 softer, so that they can be more readily broken up in the mouth. It also 

 causes the starch grains to swell up and burst, and so aids the digestive fluids 

 in penetrating into their substance. The albuminous matters are coagulated, 

 and the gummy, saccharine, and saline matters are removed. The con- 

 version of flour into dough is effected by mixing it with water, and adding a 

 little salt and a certain amount of yeast. Yeast consists of the cells of an 



