116 CHEMICAL COMPONENTS OF THE HUMAN BODY. 



alkaline, or acid. When mineral substances, whose presence is superfluous or 

 noxious, are introduced into the body, an effort is usually made for their elimi- 

 nation, by some of the excretory organs; most commonly by the kidneys. 



92. There is very strong evidence that, in all these transformations, Chemical 

 forces are alone concerned; this evidence arising, on the one hand, from the 

 nature of the changes themselves; and, on the other, from the certainty that 

 such forces must be in operation, and that their effects will be modified by the 

 peculiar conditions under which they are exerted. We have already seen that 

 many of the changes taking place within the living body can be precisely imi- 

 tated out of it, by the use of means whose actual operation is of the same kind, 

 though the modus operandi may be very different. Of this a remarkable ex- 

 ample is afforded by the process of oxidation, which is continually going on 

 within the system, and which produces a most important influence on the con- 

 dition of the products of its disintegration. When the Chemist desires to con- 

 vert one organic compound into another by oxidation, he treats it with some 

 substance (e. g. nitric acid or peroxide of lead) which readily yields oxygen ; 

 whereas, the Physiological method is altogether different, for the substance to be 

 acted on, being diffused through the circulating fluid, is exposed to the direct 

 influence of the oxygen of the air, in a state of almost infinitely minute division, 

 during the passage of that fluid through the multitudinous capillary channels 

 of the lungs. Now of the efficacy of this state of subdivision, in bringing 

 about changes which do not occur when the substances to whose attractive 

 forces these are due are simply exposed to each other en masse, we have a very 

 remarkable example in the fact that iron, when reduced from the oxide to the 

 metallic state by a current of hydrogen gas, and thus left as a very fine powder, 

 becomes spontaneously ignited by exposure to common air, and oxidizes as 

 rapidly as a piece of iron-wire would do when burned in pure oxygen or im- 

 mersed in nitric acid. This point has scarcely been sufficiently attended to by 

 Chemists, who have too readily satisfied themselves with accounting for such 

 metamorphoses by laboratory operations, without inquiring how far similar 

 agencies could be at work within the body : and we shall hereafter find that this 

 powerful oxidizing process is probably employed, not merely in the combustion 

 of materials introduced into the body, or supplied from itself, for the mainte- 

 nance of its heat, nor only, in addition, for the removal of some of the products 

 of its own disintegration, but also for the decomposition and elimination of 

 certain organic poisons, from which, when they have been introduced into the 

 body from without, it is freed through this channel, as it is from many of those 

 of a mineral nature through the kidneys. Allusion has already been made, 

 again, to the peculiar action of ferments ( 19), which tend to produce new 

 arid simpler arrangements of the elements of organic compounds, such as no 

 ordinary reagents could effect. And it has been also pointed out that the very 

 same substance in different stages of decomposition may occasion the genesis of 

 several different sets of new compounds, according to the state in which it may 

 itself happen to be when employed for this purpose. Moreover, it has been 

 also seen, in how very marked a degree the condition and the metamorphoses of 

 organic compounds are effected by the presence of very small quantities of in- 

 organic substances; but whether their influence be that of ordinary chemical 

 attraction, or that which has been termed "catalytic" power, cannot yet be 

 positively stated. It is to be remembered, moreover, that the circulating fluid, 

 which is probably the seat of most of these metamorphoses, is itself in a state 

 of constant change ; that new components are continually being introduced, on 

 the one hand from the alimentary materials, and on the other from the disinte- 

 gration of the tissues; and that such a condition must be eminently favorable 

 to the chemical metamorphosis of its organic constituents. It may be remarked, 

 moreover, that the mode in which capillarity is brought into action in the pro- 



