836 SALTS AS FOOD. [BOOK n. 



element phosphorus seems no less important from a biological 

 point of view than carbon or nitrogen; it is as absolutely 

 essential for the growth of a lowly being like Penicillium as for 

 man himself. We find it probably playing an important part 

 as the conspicuous constituent of lecithin and other complex fats 

 belonging to the nervous system, we find it prominent in the 

 peculiar body nuclein, we find it peculiarly associated with the 

 proteids ; but we cannot explain its role. The element sulphur, 

 again, is only second in importance to phosphorus, and we find it as 

 a constituent of nearly all proteids ; but we cannot foretell the 

 exact changes which would take place in the economy if all the 

 sulphur of the food were withdrawn. In the keratin of the 

 epidermis and its appendages, hairs, &c., it is probably undergoing 

 excretion, though its presence in this body may have to do with 

 the peculiar physical characters of corneous epithelium. 



We know that the various saline matters are essential to 

 health, that when they are not present in proper proportions 

 nutrition is affected. Dogs fed on food, freed as much as possible 

 from all saline matters, but otherwise abundant, with a proper 

 proportion of the food-stuffs, soon exhibit symptoms shewing that 

 the metabolism of their tissues, especially of their central nervous 

 system, is going wrong ; they suffer from weakness, soon amounting 

 to paralysis, and are often carried off by convulsions. And more 

 or less similar derangements of nutrition follow the absence or a 

 deficiency of individual salts. During starvation these various 

 salts continue to be discharged from the body; in some way or 

 other they are carried along in the metabolic stream, and their 

 presence is in some way essential to the various metabolic 

 processes; hence they need to be always present in daily food. 

 In what way it is that they thus direct metabolism we do not 

 know ; we are aware that the properties and reactions of various 

 proteid substances are closely dependent on the presence of 

 certain salts; but beyond this we know very little. The in- 

 organic salts are those, the nutritive value of which has been 

 chiefly studied by experiment ; but we have reason to believe that 

 the organic salts, or extractives, which are present in greater or 

 less quantity in all food of both vegetable and animal origin, are 

 no less essential to the proper metabolic activities of the body. 

 The undoubted connection of scurvy with the lack of fresh 

 vegetable food, other conditions helping, may perhaps turn in 

 part on this, for the evidence that the disease is due to the 

 deficiency of potash alone is not conclusive. 



Lastly, water has an effect on metabolism, as shewn, among 

 other things, by the fact that when the water of a diet is 

 increased, the urea is increased to an extent beyond that which 

 can be explained by the increase of fluid increasing the facilities of 

 mere excretion. 



