VALUE OF DIFFERENT MATERIALS OF FOOD. 247 



state of perfect solution, it is taken up at once by the simple act of physi- 

 cal absorption or endosmose, instead of requiring any preliminary pre- 

 paration or exertion of vital activity for its absorption. But there is no 

 evidence that Gelatine can ever be transformed into a proteine-compound, 

 and can thus be applied to the nutrition of the muscular and other fibrous 

 tissues ; and the presumption, derived from the result of various experi- 

 ments, is very strong the other way. 



430. The Non-azotized compounds, which are presented to us in great 

 abundance in the Vegetable kingdom, exist under various forms ; of 

 which the principal are starch, sugar, and oil. The two former may be 

 regarded as belonging to one class, the Saccharine ; because we know 

 that starch and the substances allied to it may be converted into sugar 

 by simple chemical processes, and that this transformation takes place 

 readily both in the Vegetable and Animal economy. On the other hand, 

 the Oily matters contained in vegetable and animal food, are usually 

 ranked as a distinct group of alimentary substances ; and it has been 

 maintained that, under no circumstances, has the Animal the power of 

 elaborating fatty matter from starchy or saccharine compounds. But 

 this is now known to be an unfounded limitation ; since the transforma- 

 tion of a saccharine into a fatty compound takes place in the case of 

 bees, which form wax when fed upon pure sugar, and it has been recently 

 shown that it may take place in the laboratory of the Chemist, butyric 

 acid (the fatty acid of butter) being one of the products of the fermenta- 

 tion of sugar, taking place under peculiar circumstances. It appears, 

 indeed, to be one office of the Liver to effect this transformation, as will 

 be explained hereafter. 



431. The great use of these substances in the Animal economy, is to 

 support the respiratory process, and thus maintain the temperature of 

 the body. We have seen that, in the compounds of the Saccharine group 

 (in which Starch is included), the amount of oxygen is no more than 

 sufficient to form water with the hydrogen of the substance ( 12), so 

 that the carbon is free to combine with the oxygen taken in by the lungs, 

 and thus becomes a source of calorifying power. Again, in the oily 

 matters taken in as food, the proportion of oxygen is far smaller, so that 

 they contain a large quantity of surplus hydrogen, as well as of carbon, 

 ready to be burned off in the system, and thus to supply the heat re- 

 quired. This is obviously the ordinary destination of the alimentary 

 matters belonging to these classes ; and the greatest economy in the 

 choice of diet is therefore exercised, when it is composed of azotized sub- 

 stances in sufficient amount to repair the waste 7 of the system, and of 

 non-azotized compounds which include free carbon and hydrogen in suf- 

 ficient quantity to develope (with the aid of other processes) the requisite 

 amount of heat by combination with oxygen. But if there be a deficiency 

 in either of these kinds of aliment, the body must suffer. Should the 

 supply of duly-prepared azotized matter be less than is required to re- 

 pair the waste of the albuminous and gelatinous tissues, then these di- 

 minish in bulk and in vital power, though the heat of the body may be 

 kept up to its proper standard. But if the non-azotized matter should 

 be supplied in insufficient amount, or in a form in which it cannot be 

 appropriated, the heat of the body cannot be sustained in any other way, 

 than by drawing upon the store of fat previously laid up. 



