924 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, t it has been shown that if the necessary proteins, fats, and 

 carbohydrates are supplied but the inorganic salts are omitted 

 or furnished in improper proportions the animal promptly loses 

 weight and dies. Recent dietary studies, in fact, have shown that in 

 selecting a well-balanced diet attention must be paid to the compo- 

 sition in inorganic constituents, as well as to the proportions of 

 protein, fats, and carbohydrates. In vegetable foods, for example, 

 fche ash of the leaves is quite different from that of the seed, and an 

 exclusive use of either portion of the plant might result in a dietary 

 insufficienc}^, owing to the poorly balanced inorganic ration. 



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 



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

 "Physiologie u. Pathologie des Mineral-Stoffwechsels," 1906, and von Wendt, 

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



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

 and McCoUum, "Journal of the American Medical Association," May 12, 1917. 



