CHEMISTRY OF DIGESTION AND NUTRITION. 355 



were received into the body, Some of them, however, notably the phosphates 

 and the sulphates, are formed in the course of the metabolism of the tissues, 

 and without doubt reactions of various kinds occur affecting the composition 

 of many of the salts — for example, the decomposition of the chlorides to form 

 the HC1 of gastric juice. But these reactions do not materially influence the 

 supply of energy in the body : the value of the salts lies in the general fact 

 that they are necessary to the maintenance of the normal physical and chem- 

 ical properties of the tissues and the body-fluids. Experimental investigation l 

 has shown in a surprising way how immediately important the salts are in this 

 respect. Forster fed dogs and pigeons on a diet in which the saline constit- 

 uents had been much reduced, although not completely removed. The animals 

 were given proteids, fats, and carbohydrates, but they soon passed into a 

 moribund condition. It seemed, in fact, that the animals died more quickly 

 on a diet poor in salts than if they had been entirely deprived of food. 

 Similar experiments were made by Lunin upon mice, with corresponding 

 results. He showed, moreover, that while mice live very well upon cow's milk 

 alone, yet if given a diet almost free from inorganic salts, consisting of the 

 casein and fats of milk plus cane-sugar, they soon died. Moreover, if all the 

 inorganic salts of milk were added to this diet in the proportion in which 

 they exist in the ash of milk, the mixture still failed to support life. It would 

 seem from this result that the inorganic salts cannot fulfil completely their 

 proper functions in the body unless they exist in some special combination 

 with the organic constituents of the food. In this connection it is well to bear 

 in mind that proteids as they occur in nature seem always to be combined 

 with inorganic salts, and the properties of proteids, as we know them, are 

 undoubtedly dependent in part upon the presence of this inorganic constituent. 

 We may assume that the original synthesis of the organic and inorganic 

 constituents is made in the plant kingdom, and that, in its own way, 

 the inorganic constituent of the molecule is as necessary to the proper 

 nutrition of the animal tissues as is the organic. One salt (NaCl) is 

 consumed by many animals, including man, in excess of the amount uncon- 

 sciously ingested with the food. Bunge points out that purely carnivorous 

 animals are not known to crave this salt, while the herbivora with some 

 exceptions — for example, the rabbit — take it at times largely in excess. 

 The need of salt on the part of these animals is well illustrated among the 

 wild forms by the eagerness with which they visit salt-licks. Bunge advances 

 an ingenious theory to account for the difference between the herbivora and 

 the carnivora in regard to the use of salt. He points out that in plant 

 food there is a relatively large excess of potassium salts. When these salts 

 enter the liquids of the body they react with the NaCl present and a mutual 

 decomposition ensues, with the formation of KCl and the sodium salt of the 

 acid formerly combined with the potassium, and the new salts thus formed are 

 eliminated by the kidneys as soon as they accumulate beyond the normal limit. 



1 Bunge: Physiological and Pathological Chemistry, translated by Wboldridge, L890. 



