1 66 MILK [xi 



muscles, tendons, and other portions of the body 

 which contain nitrogen in their composition can 

 only be built up by members of the protein group of 

 nutrients. But, as has been pointed out, the protein 

 group is a large one, and all its members do not 

 possess this tissue-forming power ; indeed, it is only 

 the albuminoids so called from the typical member 

 of the group, albumin, or the white of an egg which 

 possess it. 



The albuminoids, then, are the most important 

 group of nutrients. From them also is the most of 

 the fat in the animal body formed; although both 

 the fats and the carbohydrates are also capable of 

 being used in this way. The proportion in which 

 the fat in the body is derived from the three sources 

 is not known, and, indeed, varies with circumstances, 

 more especially according to the proportion in which 

 the three different classes of nutrients are present in 

 the food. As the body, more especially in certain 

 of its parts, such as the bones, blood, teeth, hair, and 

 many of the fluids, contains mineral salts (phosphates, 

 sulphates, and the chlorides of potassium, sodium, 

 calcium, and magnesium), certain mineral substances 

 are absolutely necessary. 



But another great function of food is to furnish 

 the body with the necessary animal heat. Although 

 the members of the protein group are capable of 

 acting in this way as heat-givers, and furnishing the 



