480 A MANUAL OF PHYSIOLOGY 



about 4 per cent, of proteid, 4 to 6 per cent, of fat, 4 per cent, of 

 lactose, and "j per cent, of salts. When given to infants it should 

 be diluted with water, and some sugar should be added to it. Ass's 

 milk has about the same amount of proteid, lactose and salts as 

 human milk, but less than half as much fat. It is very well borne 

 and very completely absorbed. 



As to the place of water and inorganic salts in diet, it is 

 neither necessary nor practicable to lay down precise rules. 

 In most well-settled countries they cost little or nothing; 

 very different quantities can be taken and excreted without 

 harm ; and both economics and physiology may well leave 

 every man to his taste in the matter. Salt is indeed for 

 the most part used, not as a special article of diet, but as a 

 condiment to give a relish to the food, just as a great deal 

 more water than is actually needed is often drunk in the 

 form of beverages. It is certain that the quantity of salt 

 required, in addition to the salts of the food, to keep the 

 inorganic constituents of the body at their normal amount, 

 is very small. A 3O-kilo dog obtains in his diet of 500 

 grammes of lean meat only 0'6 gramme sodium chloride, 

 and needs no more. An infant in a litre of its mother's 

 milk, which is a sufficient diet for it, gets only 0*8 gramme 

 sodium chloride. Bunge, however, has shown that the pro- 

 portion of potassium and sodium salts in the food is a factor 

 in determining the quantity of sodium chloride required. 

 A double decomposition takes place in the body between 

 potassium phosphate and sodium chloride, potassium chloride 

 and sodium phosphate being formed and excreted ; and the 

 loss of sodium and chlorine in this way depends on the 

 relative proportions of potassium and sodium in the food. 

 In most vegetables the proportion of potassium to sodium 

 is much greater than in animal food, so that vegetable- 

 feeding animals and men as a rule desire and need relatively 

 great quantities of sodium chloride. But it is stated that 

 the inhabitants of a portion of the Soudan use potassium 

 chloride instead of sodium chloride, obtaining the potassium 

 salt by burning certain plants which leave an ash poor in 

 carbonates, and then extracting the residue with water and 

 evaporating (Dybowski). A beef-eating English soldier 



