NUTRITION 1 1 5 



person needs 2-2.5 litres. The amount of water needed is 

 determined by the amount lost in the urine, sweat, and 

 expired air. 



The salts of the food in part replace the salts taken from 

 the tissue fluid by the excretory organs, and in part furnish 

 material for the formation of organic substances (nuclein, 

 haemoglobin). The following are the salts necessary as 

 foods : 



The phosphates of the alkalies are used in the building of 

 the tissues. Only in the presence of potassium phosphate 

 can the cell substance regenerate itself. 



Calcium and magnesium phosphate serve chiefly in build- 

 ing up the skeleton. 



Salts of iron are used in the formation of the red blood 

 pigment. 



The need of iron seems, as a rule, to be completely satisfied by 

 the organic iron (nucleo-proteids containing iron) which is taken 

 up with the other foodstuffs so that no other iron salts need to be 

 taken. 



The salts enumerated thus far are found in sufficient 

 quantity in the foods generally taken, so that they do not 

 need to be specially added. The case is, however, different 

 with 



Sodium chloride, which not only serves to replace the loss 

 from the body fluids, but serves, at the same time, as a con- 

 diment (see page 1 18) and is therefore eaten in much larger 

 quantities than is really necessary. The average amount of 

 NaCl taken by the adult is about 17 grams, while the real 

 need is only about 2 grams. 



The need of sodium chloride is greater among people living 

 upon vegetable food (Negro) than among those eating flesh 

 (Samoids, Tunguses). The reason for this has been sought in the 

 greater amount of potassium salts of the vegetables. The potas- 

 sium carbonate acts upon the sodium chloride in the body so that 

 sodium carbonate and potassium chloride are formed. These 

 substances are excreted by the kidneys. Hence by the partaking 

 of potassium salts the excretion of sodium and chlorine is increased 

 and therefore more sodium and chlorine must be taken up in the 

 food. 



