INORGANIC SUBSTANCES. 883 



per cent, in which the different salts of the ash occur in dried food- 

 stuffs. 1 



Animals from whose food the salts have been extracted, some- 

 times die even more rapidly than animals which have been altogether 

 deprived of food, with the supervention of various symptoms indicating 

 a disturbance of the central nervous system and of the digestive system. 2 

 This more rapid end of such animals is due, according to Bunge, 3 

 to chronic acid-poisoning, produced by the oxidation of the sulphur 

 of the proteids ; such acid being normally neutralised by the basic salts 

 (phosphates, carbonates, and alkali-albuminates) taken in with the food, 

 whereas in the absence of these, basic substances are removed from the 

 tissues to take their place. The experiments of Lunin (in Bunge's 

 laboratory) upon mice fed respectively upon salt-free food, or upon the 

 same food to which sufficient sodium carbonate was added to exactly 

 neutralise the sulphuric acid which would be formed in the oxidation 

 of the proteid of the food, seem to show that Bunge's conjecture is 

 correct ; for such animals lived considerably longer than those to which 

 no soda was given, or than those to which it was given combined with 

 chlorine. 4 This, however, is probably not the whole explanation, for in 

 both the dog and man the faculty of resisting the effects of acids in the 

 ingesta depends in part, at least, on their neutralisation by ammonia, 

 which is derived from metabolised proteid. 5 



It would appear that some at least of the mineral matters of the 

 food must be in their natural condition, which is probably that 

 of combination with the proteid substances. For Lunin found that 

 although mice will live indefinitely on desiccated milk, yet if they 

 are given an artificial food consisting of a mixture of salt-freed casein and 

 lactose, to which have been added the same inorganic salts which are 

 present in the original milk, the animals will die at about the same period 

 as if sodium carbonate alone had been added to the casein and sugar. 6 



As Bunge has pointed out, the addition of chloride of sodium to the 

 ordinary food appears to be essential to the well-being of all animals 

 the food of which contains a large proportion of potassium salts, as 

 occurs in most vegetables. In conformity with this, we find that those 

 races of mankind which subsist mainly on vegetable food find salt an 

 absolute necessity of life ; and that the same is the case with herbivorous 

 animals is shown by the fact that these are often found to travel 

 hundreds of miles to reach a place where salt is to be found (salt-licks). 

 Carnivorous animals, on the other hand, and those herbivora which 

 consume plants and herbage which do not contain a great excess of 

 potassium salts, show no such inclination to seek salt. The same is true 

 for those races of mankind who live almost exclusively on fish or flesh, 



1 Note especially the small amount of Na 2 in wheat and peas ; the large amount of 

 CaO in milk and egg yolk, and the very small amount of iron in milk. On the other 

 hand, the ash of the foetus contains a very large proportionate amount of iron. 



2 Forster, Ztschr. f. BioL, Munchen, 1873, Bd. ix. S. 297. 



3 Ztschr. f. BioL, Munchen, 1874, Bd. x. S. 130. See also "Lectures," pp. 114-118. 



* Ztschr. f. physiol. Chem., Strassburg, 1881, Bd. v. S. 31. See also Socin, ibid., 1891, 

 Bd. xv. S. 100. 



5 Schmiedeberg and Walter, Arch. f. exper. Path. u. PharmakoL, Leipzig, Bd. vii. 

 S. 148 ; Hallervorden and Coranda, ibid., Bd. xii. S. 76. 



6 Somewhat similar conclusions were arrived at by Bnnge and Socin from experiments 

 upon another artificial food, which had been first deprived of salts, but to which these 

 were afterwards added. This food, although apparently containing all needful materials 

 for nutrition, was unable to keep the mice which were fed upon it alive. 



