802 NUTRITION AND HEAT REGULATION. 



Fatal Effects of Ash-free or Ash-poor Diets. Dogs have 

 been fed (Forster) upon a diet composed of ash-free fats and carbo- 

 hydrates, and meats which had been extracted with water until 

 the salts had been much reduced. The animals were in a moribund 

 condition at the end of 26 to 36 days. It is probable that they 

 would have lived longer if deprived of food entirely, with the excep- 

 tion of water, since the metabolism of the abundant diet provided 

 aided in increasing the loss of salts from the body. Lunin has 

 described experiments which indicate that some at least of our 

 salts must be provided for us in organic combinations such as are 

 found in plant and animal foods. In his experiments he found 

 that mice lived well on a diet of dried cows' milk. If fed, however, 

 on a diet containing the organic but ash-free constituents of milk, 

 namely, sugar, fat, and casein, together with the extracted 

 salts of cows' milk, they died in 20 to 30 days. 



The Special Importance of Sodium Chlorid, Calcium, and 

 Iron Salts. Sodium chlorid occupies a peculiar position among 

 the inorganic constituents of our diet, in that it is the only one 

 which we deliberately add to our food. The other inorganic 

 material is taken unconsciously in our diet, but although sodium 

 chlorid exists also in our food in relatively large quantities we 

 purposely add more. It is estimated that the average man in- 

 gests from 20 to 30 gms. a day. This peculiarity is exhibited 

 also by many animals. The farmer provides salt for his stock and 

 wild animals visit the salt-licks constantly. Bunge has called 

 attention to the fact that among men and animals this desire for 

 salt is limited, for the most part at least, to those that use vege- 

 table food. From the accounts of travelers he shows that when 

 a purely animal diet is used there is no desire for salt ; but on a vege- 

 table diet there is a craving for it which may become very intense 

 and unpleasant when circumstances prevent its being obtained. 

 He offers an ingenious explanation for this relation. Most vege- 

 tables contain a large amount of potassium salts, and in the blood 

 these salts react with the sodium chlorid. Thus, if potassium 

 sulphate were added to the blood it would react with sodium 

 chlorid, giving some potassium chlorid and some sodium sulphate. 

 Both of these salts will be removed by the kidneys, since, except 

 in minute amounts, they are, so to speak, foreign to the blood. 

 This latter liquid will thereby lose some of its supply of sodium 

 salt, whence the craving for more in the food.* Whether or not 

 this explanation is correct, the fact which it seeks to account for 

 seems to be well established. It can not be doubted, however, that 

 under ordinary conditions we use salt in quantities much larger than 



* For an interesting discussion, see Bunge, " Physiologie des Menschen, " 

 vol. ii, p. 103, 1901. 



