152 DIGESTION. [CHAP. xxn. 



to us to be eminently practical ; and on that account we recom- 

 mend it to the attention of our readers. As water enters so largely 

 into the constitution of the body, being essential to the integrity 

 and to the vital action of the solids, and as it forms the principal 

 part of the blood, it is necessary that all animals should be supplied 

 with liquid food in some shape. Accordingly, water, either alone 

 or holding important nutrient elements in suspension or solution, 

 forms part of the food of all animals the aqueous group of ali- 

 mentary materials of Prout. 



A large number of substances derived from the vegetable king- 

 dom, constitute the saccharine group of Dr. Prout. These are cha- 

 racterized by being composed of carbon, united to hydrogen and 

 oxygen, in the proportions in which these latter elements form 

 water; the proportion of the carbon varying from 30 to 50 per 

 cent.* This group comprehends sugars, starch, gums, vinegar. 

 These substances are contained in vegetables of various kinds, 

 sometimes forming their principal constituent, and at other times 

 combined with other nutrient principles. 



The oily or oleaginous group of alimentary substances, compre- 

 hends all those substances whose composition consists of olefiant 

 gas and water. It includes the various fats and oils, as well as 

 alcohol. It resembles in ultimate constitution the saccharine 

 group; the proportion of carbon in the various substances con- 

 tained in it, varying from 60 to 80 per cent. 



A fourth group, the albuminous, is made up of all those sub- 

 stances which contain nitrogen such as fibrine, gelatine, albumen, 

 caseine, vegetable gluten. All the materials which make up this 

 group are derived generally from the animal kingdom, with the ex- 

 ception of the last, which is contained in great abundance in wheat ; 

 similar, if not identical, principles exist in vegetables. Wheat, in- 

 deed, consists of two substances one referable to the saccharine 

 group, the other to the albuminous, the former consisting of starch, 

 the latter of gluten. This fact was recognised more than a century 

 ago (an. 1742) by Beccaria, who assigned the glutinous portion to 

 the nourishment of the nitrogenous ^issues of the body.f 



In milk, we find a natural combination of all the various sub- 

 stances employed for nutrition; and it is a fact of the highest 

 interest, that this product of animal secretion, elaborated for the 

 nourishment of the young, should contain one or more substances 

 for each of the above-named groups of alimentary materials. 



* See Promt's papers in the Phil. Trans. 

 t Dr. Thomson, Med. Chir. Trans. 1846. 



