118 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



phosis of albumen into fibrin; and of that still more decided change which 

 subsequently takes place, when the fibrous tissues are converted, in the act of 

 formation, into the substance which yields gelatin. For, as already pointed out, 

 although the Chemist has not yet succeeded in imitating this metamorphosis, 

 yet there are circumstances which indicate that such a fundamental relation ex- 

 ists between the protein-compounds and gelatin as leaves no right to assume 

 that any other than chemical forces are concerned in it. 



95. But with the changes directly concerned in the development of living 

 tissue, Chemistry would seem to have nothing whatever to do. The substance 

 of Muscle, for example, is chemically the same with the Albumen of the blood ; 

 and the whole difference between the organized structure possessed by the 

 former and the amorphous coagulum formed by the latter, between the marvel- 

 lous activity of the one and the passive inertness of the other, must be attributed 

 to Vital force alone. Now it is one of the chief peculiarities of this Vital force, 

 that it is able, so long as it is capable of being fully exerted, to resist and keep 

 at bay the influence of those Chemical and Physical forces, which would tend, 

 were it not for this property of the living substance, to effect its speedy disinte- 

 gration and decay. Of this we have a most characteristic and apposite example, 

 in the case of a seed that has been brought to the surface of the soil, after hav- 

 ing been buried for a long lapse of years or centuries in the earth. Whilst it 

 remained in complete seclusion from moisture and oxygen, and was kept at a 

 low temperature, no appreciable alteration took place in it ; but so soon as it is 

 exposed to warmth, and to the contact of air and water, it must begin to change 

 its passive existence giving place to a state either of growth or of decay, 

 according as it has retained, or has lost, its vital properties. For the very 

 agents which are most effectual in stimulating it to vital activity, and which 

 afford the conditions, dynamical and material, whereby the seed develops itself 

 into the plant, are those which, if the seed be no longer capable of germination, 

 most favor its decay, reducing its organic components back to the condition of 

 inorganic compounds. This peculiar attribute of living substances will be more 

 fully considered in the next Chapter. 



96. Immediately, however, that we pass the confines of Life, we re-enter the 

 domain of Chemistry ; for so soon as the vital activity of the living tissues has 

 ceased, their materials again become entirely subject to Chemical forces ; and 

 all the metamorphoses which we have been occupied in tracing out tending, 

 as they do, to reduce the organic compounds with which they commence, lower 

 and lower in the scale, until these are restored to the forms of simple binary 

 composition from which their elements were at first derived can scarcely be 

 regarded in any other light than as the result of ordinary Chemical agencies. 

 Thus, then, according to the view here advocated, the Life of each part is de- 

 pendent upon Chemical operations, in so far as it is by these that its nutrient 

 materials are prepared, and the products of its decomposition are carried away ; 

 but the application which it makes of such materials to the production of new 

 organized tissue, and the various actions which that tissue then exerts in virtue 

 of its organization, are not only incapable of being explained on Chemical prin- 

 ciples, but often take place in direct antagonism to Chemical forces. 1 



1 It has seemed advisable to attempt thus to mark out the operation of Chemical Forces 

 in the living body, since the prevalent notions on this subject appear to the Author either 

 erroneous or vague. The accumulating evidence of the purely chemical nature of many 

 of those changes of composition, which were formerly set down as the results of " vital affi- 

 nity," has led many Chemists to the idea that the whole series of Vital operations is to be 

 explained upon Chemical principles ; and the notion of Vital force has been set aside as a 

 physiological fiction, for which there is no longer any pretence. Feeling satisfied, how- 

 ever, that Vital force has as certain an existence, and as definite a sphere of operation, as 

 Chemical Affinity, the Author will make it his endeavor, in this Treatise, so to analyze 

 the phenomena of the living body, as to trace the respective limits of the operation of each 

 of these powers. 



