CHAPTER XLIX. 



NUTRITIVE VALUE OF THE INORGANIC SALTS AND 

 THE ACCESSORY ARTICLES OF DIET. 



The Inorganic Salts. The body contains in its tissues and 

 liquids a considerable amount of inorganic material. When any 

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

 the bones, which are rich in mineral material, the average amount 

 of ash in the body amounts to about 0.1 per cent, of its weight. 

 It consists of chlorids, phosphates, sulphates, carbonates, 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, on the contrary, have no importance 

 from the former standpoint. Whatever chemical changes they 

 undergo are not attended by any liberation of heat energy, none 

 at least, of sufficient 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 im- 

 portant 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 irritability. Even the proteids 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 

 proteids 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 and the irritability 

 of muscular and nervous tissues. The special importance of the 

 iron salts for the production of hemoglobin is also evident without 

 comment. The nutritive importance of the salts in the diet has 

 been demonstrated by direct experiment. 

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