316 STUDIES IN ADVANCED PHYSIOLOGY. 



entirely to fats, or even to fats, starches and sugars. While 

 the fats are sources of greater energy than the carbohy- 

 drates, and so better suited for colder climates, they seem 

 not so well suited for temperate climates, and not at all for 

 tropical regions. Even in the latitude of Indiana, the fats 

 and oils have not nearly the general food value of the car- 

 bohydrates. Used to supplement the proteids, starches and 

 sugars, they are of course very desirable. The commoner 

 examples of the hydrocarbons are butter, lard, tallow, and 

 the vegetable oils. 



5. The Inorganic Salts. In the common use of the 

 term " food," such articles as common and other inorganic 

 salts are not included, but there is as much of a necessity 

 for the presence of some of these salts to make possible the 

 normal functions of the body as there is that proteids, sugars 

 and fats shall replace the waste. With the exception of 

 common salt, which is added as a special ingredient, usu- 

 ally however more for the palate than for its physiological 

 value, the other inorganic salts reach us as regular ingredi- 

 ents of the foods. In nearly all of our solid foods there is 

 a small proportion of mineral matter. This may easily be 

 demonstrated by burning bits of these foods. There are 

 practically no foods which do not leave, when burned, bits 

 of ash. This ash of course constitutes the mineral salts 

 contained in the original substance. While all of these salts 

 do not find their way into the body, the body is able to dis- 

 solve and assimilate such of them as are especially needed 

 in the work of the tissues for the building up of mineral 

 constituents of such tissues as bone or enamel. A few of 

 the commoner mineral salts which are required in the body 

 are here given. 



For the growth of bone there are required salts of mag- 

 nesium and calcium (lime) ; for the haemoglobin of the 

 blood, traces of iron ; for the blood and lymph of the body, 

 considerable quantities of common salt\ as an integral por- 

 tion of the red corpuscles and other tissues, potash salts. 



