68 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



GMJTIN. CHONDRIN. 



Mulder. Scherer. Mulder. Scherer. 



Carbon . . . 50.4 50.8 50.0 50.7 



Hydrogen ... 6.7 7.1 6.6 6.9 



Nitrogen . . . 18.3 18.3 14.4 14.7 



^Yi 611 1 24.6 23.8 29.0 27.7 



Sulphur / 



100.0 100.0 ' 100.0 100.0 



35. It is remarkable that, notwithstanding the very large proportion of the 

 entire mass of the body, which is formed by the Gelatigenous tissues, no Gelatin 

 should be detectable either in the Blood, or in any of the healthy fluids ; and 

 this fact seems to indicate that the transformation of protein-compounds into 

 gelatin, which must take place wherever the food does not contain that substance 

 (as in the case of herbivorous animals and of the embryo within the egg), is 

 effected in the very act of their conversion into fibrous tissue a view which 

 appears to derive probability from the various facts already stated respecting the 

 properties of Fibrin ( 25, 27). If this be true, it seems highly improbable 

 that the gelatigenous tissues are ever produced in any other way, or that gelatin 

 employed as food can ever acquire even the low degree of organization which 

 they exhibit; and reasons will be hereafter given for the belief, that this sub- 

 stance cannot be truly regarded as a histogenetic material, but must be looked 

 upon merely as a pabulum for the combustive process (see CHAP. vn.). Some 

 Chemists, indeed, maintain, that Gelatin is rather a product of the operation 

 practised to separate it, than a real constituent of the living solids ; but this 

 idea is inconsistent with several important facts. Thus, the gelatigenous tissues 

 will exhibit, without any preparation, the best-marked of the chemical properties 

 by which Gelatin is characterized that of forming an insoluble compound with 

 tannic acid ; and the tanno-gelatin, which may be obtained by precipitating gela- 

 tin from its solution, appears to be identical with that which results from the 

 action of tannin on animal membrane, in every respect save the want of its 

 organic structure. A similar precipitate is thrown down, as Dr. Alfred Taylor 

 has recently shown, by adding tannic acid to the solution obtained by acting on 

 Skin with acetic or oxalic acid. And further, the composition of gelatin, and 

 that of the gelatigenous tissues (allowance being made for the presence of other 

 ingredients in the latter), are found by ultimate analysis to be identical. The 

 fact appears to be that there is somewhat of the same difference between gelatin, 

 chemically considered, and the fibrous tissues, bone, &c. from which it is ex- 

 tracted, that exists between albumen and muscular fibre ( 21); chemically 

 they are identical, but the molecular arrangement of the particles has been 

 altered by organization, so that the operation of solvents is required to bring 

 back the organic compounds to their original structureless condition. And this 

 view harmonizes well with the fact, that the tissues which are most readily dis- 

 solved by hot water, and on which cold water has the most action (such as those 

 of the air-bladder of the fish), are those which have the least definite organic 

 structure; whilst, on the other hand, those of which the fibrous structure is 

 most complete, require the most prolonged action of hot water to gelatinize them. 

 There is a difference, too, in the characters of the gelatin obtained from these 

 different sources ; for that which is so readily yielded by the fish's air-bladder, 

 and is known as "isinglass," never forms a strong glue, even when quite dry ; 

 so also the gelatin of the skin of young animals, which forms " size/' though 

 setting more firmly than isinglass, cannot be advantageously employed by the 

 carpenter ; his hard " glue" being all obtained from the skin, bones, &c. of 

 adults. These differences have been imputed by Dr. Prout to diversities in the 

 quantity of water held in combination by the gelatin. The extreme difficulty 



