CHAPTER XLIX. 



PfUTRITIVE VALUE OF THE INORGANIC SALTS AND 

 THE ACCESSORY ARTICLES OF DIET. 



The Inorganic Salts. — The body contains in its tissues and 

 fiquids a considerable amount of inorganic material. When any 

 organ is incinerated this material remains as the ash. If we in- 

 clude the bones, which are rich in mineral matter, the average 

 amount of ash in the body amounts to about 4.3 to 4.4 per cent, 

 of its weight. The bones, however, in the adult contain most of 

 this ash (five-sixths). In the soft tissues, like the muscle, the ash 

 constitutes about 0.6 to 0.8 per cent, of the moist weight. The 

 ash consists of chlorids, phosphates, sulphates, cai'bonates, fluorids, 

 or silicates of potassium, sodium, calcium, magnesium, and iron; 

 iodin occurs also, especially in the thyroid tissues. In the liquids 

 of the body the main salts are sodium chlorid, sodium carbonate, 

 sodium phosphate, potassium and calcium chlorid or phosphate. 

 In considering the organic foodstuffs weight was laid upon their 

 value as sources of energy, as well as upon their function in con- 

 structing tissue. The salts have no importance from the former 

 standpoint. Whatever chemical changes they undergo are not 

 attended by any hberation of heat energy — none at least of suffi- 

 cient importance to be considered. They have, however, most 

 important functions. They maintain a normal composition and 

 osmotic pressure in the liquids and tissues of the body, and by 

 virtue of their osmotic pressure they play an important part in 

 controlling the flow of water to and from the tissues. Moreover, 

 these salts constitute an essential part of the composition of living 

 matter. In some way they are bound up in the structure of the 

 living molecule and are necessary to its normal reactions or irrita- 

 bility. Even the proteins of the body liquids contain definite 

 amounts of ash, and if this ash is removed their properties are 

 seriously altered, as is shown by the fact that ash-free native pro- 

 teins lose their property of coagulation by heat. The globulins 

 are precipitated from their solutions when the salts are removed. 

 The special importance of the calcium salts in the coagulation of 

 blood and the curdling of milk has been referred to, as also the 

 peculiar part played by the calcium, potassium, and sodium salts 

 in the rhythmical contractions of heart muscle, the irritability 

 of muscular and nervous tissues, and the permeability of the 

 capillary walls and other membranes. The special importance of 



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