66 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



tissue seems to be dependent, not merely upon the blood which circulates through 

 it, but also upon the contents of its tubular fibres ; so also does the hue of the 

 vesicular element of nervous tissue depend partly upon the pigmentary matter 

 contained within its cells. Tt does not seem, then, to be an unreasonable sur- 

 mise, that the hsematin of the blood-corpuscles is a substance which is being 

 prepared by them for the nutrition of these tissues; and this idea is confirmed 

 by the special relation which seems to exist between the presence of a large 

 proportion of corpuscles in the blood, and the nervo-muscular power of the 

 animal ( 147). Nearly allied to haematin is a substance to which the term 

 Haematoidin has been given, and which may be regarded with probability as 

 haematin in a state of retrograde metamorphosis. This is found in sanguineous 

 effusions, such as those in the substance of the brain or skin, or those produced 

 by the bursting of the Graafian follicles for the extrusion of the ova; and it 

 presents itself most characteristically in the form of rhombohedric crystals, of 

 a yellowish-red or ruby color, although it frequently occurs in the amorphous 

 condition of granules and irregular masses. This substance has not yet been 

 obtained in a state sufficiently pure, and in a quantity large enough, to admit of 

 its being subjected to a rigid examination ; but it has been ascertained to be in- 

 soluble in alkalies, and to behave differently from haematin with other reagents. 

 Haematoidin has been inferred by Virchow, from his recent investigations, 1 to 

 be a compound of haematin and some protein substance, the latter probably 

 forming the crystalline, and the former the coloring portion of the compound ; 

 and this seems the more likely, since Reichert has found an albuminous sub- 

 stance, in the form of tetrahedral crystals, in extra vasated blood. It seems 

 probable, further, that haematoidin is a stage of transition between the blood- 

 pigment and the coloring matters of the bile, namely, cholepyrrhin and biliful- 

 vin ( 70). 



2. Gelatinous Compounds. 



32. A large proportion, perhaps not less than half, of the tissues of the body 

 of Man, as of that of the higher animals generally, is composed of a substance, 

 which, when these tissues are acted on by boiling water, dissolves in it, and 

 forms a jelly on cooling. Some tissues dissolve readily in this manner, and 

 leave scarcely any residue; whilst others require a longer coction, and a larger 

 proportion of insoluble matter remains. The substance thus obtained from 

 bones, cartilages, tendons, ligaments, skin, mucous and serous membranes, &c. 

 is known under the generic appellation of Gelatin; there are, however, two 

 forms of it, one of which is distinguished as glutin or gelatin-proper, whilst the 

 other is known as chondrin. Although differing in their ultimate composition 

 and in their behavior with reagents, these two substances agree in certain cha- 

 racteristic peculiarities, by which they are distinguished from the protein-com- 

 pounds. These are their sparing solubility in cold water, the contact of which, 

 however, makes them swell up and soften; their ready solubility in hot water, 

 with the formation of a jelly as the solution cools, this being more or less stiff 

 according to the source from which the Gelatin has been obtained, and the pro- 

 portion of it which has been dissolved; and the readiness with which both forms 

 are thrown down by tannic acid and chlorine-water, whilst they are unaffected 

 by ferrocyanide of potassium. 



33. Glutin is the form of gelatin which is yielded on boiling by the White 



from the lungs to the tissues (being then in the state of peroxide), and of carbonic acid 

 from the tissues to the lungs (being then in the state of carbonate of the protoxide) is 

 not now held by any chemist of repute, and ought to be entirely abandoned. 

 1 See "Ann. der Chem. und Pharm.," band Ixxviii. p. 353. 



