ALBUMINOUS COMPOUNDS. Ill 



their properties. Caseine appears even to surpass Aljbumen in its power 

 of combining with the phosphates of lime and magnesia, and of render- 

 ing them soluble. 



173. Albumen and Caseine, then, may be regarded as constituting 

 the raw materials, at the expense of which the organized tissues of the 

 Animal fabric are built up ; and we have sufficient evidence, in the de- 

 velopment of the Chick from the egg, and of the young Mammal from 

 milk, that they may be transformed into any of the proteine-compounds 

 which are to be found in the Animal body. There is good ground to 

 believe, however, that, for the formation of all the Animal tissues, the 

 presence of fatty matter, as well as of an albuminous compound is es- 

 sential ; and it is a circumstance worthy of note, that in both the fore- 

 going cases, fatty matter is mingled with the albumen, in the aliment 

 destined for the development of the young animal. This subject, how- 

 ever, will be more fully discussed hereafter. 



174. The Animal derives the materials of its nutrition, however, not 

 only from the Albuminous compounds furnished by flesh, eggs, and milk, 

 but also from those which are supplied by the Vegetable kingdom. Every 

 growing Plant, as already mentioned (12), forms albuminous compounds 

 by the combination of inorganic elements, as the pabulum of its own 

 tissues ; but many Plants generate them in much larger proportion, and 

 store them up in their cells ; and it is from such, that Animals derive 

 their largest supply of nutritive material. Thus the gluten of wheat, or 

 the tenacious mass which is left after the removal of the starch by wash- 

 ing, is principally composed of a substance which is closely allied in 

 composition and properties to the Albumen of animals ; being moderately 

 soluble by water, coagulated by heat, and precipitated by acids (except 

 the phosphoric and acetic) and by metallic salts ; and this is designated 

 Vegetable Albumen. From the seeds of Leguminous plants a substance 

 termed Legumin may be separated, which corresponds with Caseine in 

 not being precipitated by heat, and also in the absence of phosphorus ; 

 hence it is sometimes designated as Vegetable Caseine. Various other 

 modifications of the albuminous principle are found in Plants ; but the 

 foregoing are the most important in their relations to the nutrition of 

 Animals. Like flesh, cheese, &c., they are reduced by the digestive 

 process to the state of soluble Albumen ; and in this form they are taken 

 up, and carried into the circulation. 



175. Next in importance to the Albuminous compounds as a consti- 

 tuent of the Animal fabric, is G-elatine ; which is obtained by the action 

 of boiling water on White Fibrous tissue^ and on the various membranes, 

 &c., of which this is the chief component. The composition of Gelatine 

 is much simpler than that of the Proteine-compounds, so far, at least, 

 as regards the number of atoms of its several elements ; for it consists 



3 Carbon, 10 Hydrogen, 5 Oxygen, 2 Nitrogen. This composition 

 is the same, whether the Gelatine be obtained from isinglass, from fibrous 

 membranes, or from bones. The distinctive characters of Gelatine are 

 its solubility in warm water, its coagulation on cooling into a uniform 

 jelly, and its formation of a peculiar insoluble compound with Tannic 

 acid. Gelatine is very sparingly soluble in cold water ; though pro- 

 longed contact with it will cause the Gelatine to swell up and soften. 



