CHAP, v.] NUTRITION. 455 



it has been thought however that cane-sugar is rather more 

 fattening than starch. 



The Effects of Gelatine Food. It is a matter of common 

 experience that gelatine will not supply the place of proteids as a 

 constituent of food. Animals fed on gelatine together with fat or 

 carbohydrates die very much in the same way as when they are fed 

 on non-nitrogenous material alone. Nevertheless it would appear, 

 as might be expected, that the presence of gelatine in food is not 

 without effect. Thus nitrogenous equilibrium is established at a 

 lower level of real proteid food when gelatine is added. In a dog, 

 moreover, fed on a diet of gelatine and fat the excess of nitrogen 

 in the excreta over that in the ingesta is less, than when the same 

 dog is fed on a diet of fat alone ; that is to say, the gelatine has 

 sheltered from metabolism some proteid constituents of the body ; 

 and the consumption of fat also seems to be lessened by the presence 

 of gelatine. These facts become intelligible if we suppose that 

 gelatine is rapidly split up into a urea and a fat moiety, in the 

 same way that we have seen a certain quantity of proteid material 

 to be. It is this direct destructive metabolism of proteid matter 

 which gelatine can take up ; it seems however unable to imitate 

 the other function of proteid matter, and to take part in the 

 formation of living protoplasm. What is the cause of this differ- 

 ence, we cannot at present say. 



The Effects of Salts as Food. All food contains, besides the 

 potential substances which we have just studied, certain saline 

 matters, organic and inorganic, having in themselves little or no 

 latent energy, but yet either absolutely necessary or highly bene- 

 ficial to the body. These must have important functions in 

 directing the metabolism of the body : the striking distribution of 

 them in the tissues, the preponderance of sodium and chlorides in 

 blood-serum and of potassium and phosphates in the red corpuscles 

 for instance, must have some meaning ; but at present we are in 

 the dark concerning it. The 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, we find 

 it peculiarly associated with the proteids ; but we cannot explain its 

 rdle. The element sulphur, again, is only second to phosphorus, and 

 we find it as a constituent of nearly all proteids; but we cannot 

 tell what exactly would happen to the economy if all the sulphur 

 of the food were withdrawn. We know that the various saline 

 matters are essential to health, that when they are not present in 

 proper proportions, nutrition is affected, as is shewn by certain 

 forms of scurvy; we are also 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. 



