OPERATION OF CHEMICAL FORCES IN THE LIVING BODY. 113 



being intimately blended with this in an early stage of their formation. Of 

 this we have a notable example in the case of Muscular tissue ; but the cell- 

 walls of all other textures would be found, if they could be entirely freed from 

 their contents, to have the same composition. Even if they be altogether chemi- 

 cally identical, however, the molecular condition of the particles composing the 

 amorphous coagulum and the living cell must be entirely different; and the 

 latter exhibits distinctive vital properties, in virtue of the organizing process to 

 which its material has been subjected. Not merely the cell-walls, but the cell- 

 contents of these tissues (with the exception of those concerned in the act of 

 excretion), seem to be derived from the Albuminous or from the Fatty constitu- 

 ents of the blood : this seems clear, for example, in regard to the globulin and 

 hsematin of the red corpuscles of the blood, and the horny matter of the epider- 

 mis and its appendages, which must have their source in the former ; and also 

 with respect to the contents of the adipose and nervous vesicles, which must be 

 drawn wholly or in part from the latter. Whether, in the construction of the 

 tissues of this class, the Albumen of the blood may serve directly as the pabulum 

 for the production of cells, or whether it must needs pass first through the con- 

 dition of Fibrin, cannot be distinctly affirmed ; there is no positive evidence in 

 support of either proposition ; but the probabilities appear to the Author on the 

 whole to favor the former view. 



in. The great mass of the gelatigenous tissues of the body, whose texture is 

 simply fibrous, is also derived from the albuminous element of the Blood; but 

 this passes through the intermediate condition- of Fibrin, which may be regarded 

 as a substance endowed with the power of self-development into a low form of 

 organized structure, and therefore as having already undergone a vitalizing in- 

 fluence. There is no sufficient reason to believe that Gelatin employed as food 

 can ever be applied even to this purpose in the body ; since all that we know of 

 the genesis of the simple fibrous tissues indicates that, in assuming their charac- 

 teristic structure, they pass through gradations similar to those which we witness 

 in the production of the adventitious tissue of fibrinous exudations. 



IV. When the death and disintegration of the tissues again bring their com- 

 ponents under complete subjection to Chemical forces, an entirely different series 

 of metamorphoses takes place, tending to degrade these components towards the 

 condition of inorganic compounds. They would seem to resolve themselves into 

 two classes of substances ; on the one hand, saccharine, oleaginous, and resin- 

 ous matters, analogous to those of plants, in which carbon predominates ; on 

 the other, a set of compounds peculiar to animals, of which nitrogen is the cha- 

 racteristic ingredient. From the albuminous constituent of muscle, for example, 

 there is direct evidence that fat, sugar, and lactic acid may be generated on the 

 one hand; on the other, creatine, and (probably through this creatine) urea, 

 with the rest of the highly-azotized components of the urinary excretion. The 

 sugar generated by the agency of the liver, from the products of the waste or 

 disintegration of the system that are contained in the blood, seems to be at once 

 employed in supporting the combustive process by which the animal heat is 

 maintained. The fat may be directly applied to the same purpose, or may be 

 stored up in the cells of Adipose tissue for future use. The peculiar resinous 

 acids of the bile, which are probably formed from the same source, appear to 

 fulfil, in part at least, a similar destination, after having been made subservient 

 to other purposes. The lactic acid, chiefly generated in the substance of the 

 muscles (probably by the metamorphosis of a saccharine compound, which may 

 be looked on as the immediate product of their disintegration), is in like man- 

 ner destined to be carried off by the respiratory process, though a part of it 

 may first be rendered subservient to the digestive operation. But if the respira- 

 tory process should not be sufficiently active to remove these highly-carbonized 

 compounds from the blood, we may find the lactic and hippuric acids in the urine, 

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