550 DIGESTION. 



that gelatin is not convertible into a proteinaceous substance; and hence 

 it is not classed by them amongst the elements of nutrition; yet it con- 

 tains an unusual amount of nitrogen. It has been affirmed, that all 

 nitrogenized food, according to the above classification of Liebig, is 

 reduced in the stomach to the form of albumen; which is said to resemble 

 the gum of plants in being the raw material, as it were, out of which 

 the various fabrics of the body are constructed. Yet this is not demon- 

 strated; and it is probable that the conversion into albumen takes place 

 mo^e especially in the chyliferous vessels. 



The alimentary substances, employed by man, have generally been 

 classed either according to the ultimate chemical elements entering into 

 their composition; or to the chief proximate principle or compound of 

 organization.. In the former case, they have been grouped into : 1 ? 

 those that contain nitrogen, carbon, hydrogen, and oxygen; 2, those 

 that contain carbon, hydrogen, and oxygen; and 3, those that contain 

 neither nitrogen nor carbon. The first class will comprise most animal 

 and many vegetable substances; the second, vegetable substances chiefly; 

 whilst water is perhaps the only alimentary matter that belongs to the 

 third. 



The division proposed by M. Magendie, 1 and adopted by Dr. Paris, 2 

 is according to the proximate principles, which predominate in the ali- 

 ment. 



1. Jlmylareous aliments; wheat, barley, oats, rice, rye, Indian corn, potato, sago, salep, peas, 

 haricots, lentils, &c. 



2. Mucilaginous aliments; carrot, salsify, beet, turnip, asparagus, cabbage, lettuce, artichoke, 

 melon, &c. 



3. Saccharine aliments ; the different kinds of sugar, figs, dates, raisins, &c. 



4. Acidulous aliments ; the orange, currant, cherry, peach, raspberry, strawberry, mulberry. 



grapes, prunes, pears, apples, tornatos, &c. 

 5. Oily and fatty cocoa, olives, sweet a 



sweet almonds, hazelnuts, walnuts, animal fats, oils, but- 

 ter, &c. 



6. Caseous aliments; the different species of milk, cheese, &c. 



7. Gelatinous aliments ; the tendons, aponeuroses, skin, areolar tissue, the flesh' of very 

 young animals, &c. 



8. Albuminous aliments ; the brain, nerves, eggs, &c. 



9. Fibrinous aliments ; comprehending the flesh and blood of different animals. 



To these proximate principles gluten may be added, which has been 

 termed the most animalized of vegetable principles. According to Dr. 

 Prout, 3 it is separable into two portions, analogous to gelatin and albu- 

 men. It is very generally met with, although only in small proportion, 

 in the vegetable kingdom ; in all the farinaceous seeds, in the leaves 

 of cabbage, cress, &c. ; in certain fruits, flowers, and roots, and in the 

 green fecula of vegetables in general ; but it is especially abundant in 

 wheat, and imparts to wheaten flour the property of fermenting and 

 making bread. Of the nutritious properties of gluten, distinct from 

 other principles, we know nothing precise : the superior nutritious 

 powers of wheaten flour over those of all other farinaceous substances 



1 Precis, &c., ii. 34. 



2 A Treatise on Diet, 3d edit., p. 182, Lond., 1837; and art. Dietetics, in Cyclopaedia of 

 Practical Medicine, Amer. edit., Philad., 1845. 



3 Chemistry, Meteorology, and the Function of Digestion, (Bridgewater Treatise,) Amer. 

 edit., p. 558, Philad., 1834. 



