922 NUTRITION AND HEAT REGULATION. 



the iron salts for the production of hemoglobin is also evident with- 

 out comment. There can be no doubt, in fact, that each one of the 

 salts of the body has a special nutritive value and a special met- 

 abolic history. The time will doubtless come when the special 

 importance of the potassium, sodium, calcium, and magnesium will 

 be understood as well, at least, as we now understand the signifi- 

 cance of iron, and quite possibly this knowledge will find a direct 

 therapeutic application, as in the case of iron.* 



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 

 helped to increase the loss of salts from the body. So also in the 

 numerous experiments made upon growing rats fed upon artificial 

 diets, f it has been shown that if the necessary proteins, fats, and 

 carbohydrates are supplied but the inorganic salts are omitted the 

 animal promptly loses weight and dies. 



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 10 to 20 gms. a day. This amount seems to be in excess 

 of the actual necessities of the body, since on experimental diets 

 individuals have been kept in good condition when the total 

 content in sodium chlorid was reduced to one or two grams. 

 This desire for salt is exhibited also by many animals. The 

 farmer provides salt for his stock and wild animals visit the salt- 

 licks at intervals. Bunge has called attention to the fact that 

 among men and animals the desire for salt is limited, for the most 

 part at least, to those that use vegetable 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 vegetable diet there is a craving for 

 it which may become very intense and unpleasant when circum- 

 stances prevent its being obtained. He offers an ingenious 

 explanation for this relation. Most vegetables contain a large 

 amount of potassium salts, and in the blood these salts react with 



* For a brief summary of facts and speculations, see Alba and Neuberg, 

 "Physiologic u. Pathologic des Mineral-Stoffwechsels," 1906, and von Wendt, 

 "Handbuch d. Biochemie," 4, 561, 1911. 



f Osborne and Mendel, "Journal of Biological Chemistry," 13, 233, 1912. 



