* THE NUTRITIVE VALUE OF FOOD 1061 



able to utilize the former as tissue-protein and to burn the latter to 

 produce heat. In view of the larger body-surface of the infant and 

 its more intense metabolism, such a relationship is rather to be ex- 

 pected. Milk is also rich 'in calcium and phosphorus, a peculiarity 

 which greatly favors the growth of the skeleton. 



The Inorganic Salts. — So far special attention has been paid to 

 the carbohydrates, fats and proteins. It is to be noted, however, 

 that an animal which receives these foodstuffs without the salts, 

 succumbs even more rapidly than one fed with an absolutely inade- 

 quate diet. Evidently, the inorganic constituents are as important 

 for the maintenance of life as the organic constituents, and this in 

 spite of the fact that they do not yield energy. They are absolutely 

 essential to the body for the reason that they help in maintaining the 

 composition and osmotic pressure of the body-fluids and determine, 

 therefore, the interchanges of its metabolites. Secondly, they form 

 essential constituents of the frame-work of the body and even enter 

 into the composition of its soft parts. Thus, it will be found that 

 the incineration of the body yields about 4.3 to 4.4 per cent, of its 

 weight in ash. Of this amount, five-sixths must be apportioned to 

 the bones and one-sixth to the soft parts. The ash consists of the 

 chlorids, phosphates, sulphates, carbonates, fluorides and silicates of 

 potassium, sodium, calcium, magnesium and iron. Besides, iodin occurs 

 in the tissue of the thyroid gland. It is also evident that the potassium 

 salts belong more particularly to the organized elements of the tissues, 

 whereas the sodiu'm salts are more directly concerned with the com- 

 position of the body-fluids, and the calcium salts with that of the bones. 



In the latter case, it has been demonstrated beyond doubt that a 

 diet poor in calcium gives rise to rickets, a condition characterized by 

 a deficient and imperfect growth of the bones. In adult life, most of 

 the calcium ingested is again excreted in the feces and urine, although 

 an excessive storage may result later on which leads to a brittle condi- 

 tion of the bones and calcareous infiltrations of different tissues, such 

 as the walls of the blood-vessels. Iron enters the body in organic 

 combination, and it is still a much debated question whether inorganic 

 iron can actually be taken up and converted into so complex a sub- 

 stance as hemoglobin. 



Bunge^ has called attention to the fact that man and the carnivor- 

 ous animals have no especial longing for salts, whereas the herbivora 

 and vegetarians seek it eagerly. With the exception of sodium chlo- 

 rid, however, these salts are taken into our system unconsciously 

 in combination with the different foodstuffs, but the addition of con- 

 siderable amounts of the former to our food does not seem to be a 

 necessity, inasmuch as 1 to 2 grm. of it suffice for ordinary purposes. 

 Consequently, the daily ingestion by the average man of 10 grm. of 

 this salt may rightly be considered to be far in excess of his actual 

 needs. Bunge explains this large intake of sodium chlorid by saying 

 1 Physiol, des Menschen, 1901. 



