136 OF THE STRUCTURAL ELEMENTS OF THE HUMAN BODY. 



actions which it excites. So, again, if we observe the operation of other agen- 

 cies than those to which reference has hitherto been principally made, we notice 

 that they either modify its vital action, or entirely destroy its vital activity. 

 Thus, a moderate current of Electricity appears to promote or retard the nutri- 

 tive or other operations, according as it favors or antagonizes the chemico-vital 

 changes which they involve ; 4 whilst a violent shock is at once destructive of 

 life, a more powerful discharge being required as the bulk of the animal is 

 greater. So, again, we find that various Chemical agents exert a very definite 

 influence on the living body ; their forces not being kept at bay by its Vital 

 powers, but manifesting themselves either in the modification of its vital opera- 

 tions, or in the destruction of its living tissue. Of the former class of effects, 

 we have a good illustration in the action of what are termed the irritant poisons ; 

 these, for the most part, being substances which are known to have a definite 

 chemical relation to the components of the living tissues, and which tend, by 

 entering into new combinations with them, to interfere with those changes in 

 which vital activity essentially consists. Thus, Arsenic and Corrosive Sublimate 

 form combinations with Albumen, of such stability that they are among the 

 most perfect preservatives of dead tissues which we possess; and hence, even if 

 they do not absolutely withdraw the Albuminous constituents of the living tis- 

 sues from their normal combinations, tkey tend to do so, and by thus interfering 

 with the action of the vital forces, occasion that perversion of the nutrient 

 operations which manifests itself as Inflammation. 3 A more energetic Chemical 

 action is exerted, however, by the Corrosive poisons, which operate upon the 

 living tissues, not in modifying their vital activity, but (by completely changing 

 the state of their organic constituents) in putting a complete and entire check 

 to it; and there is no reason to regard the Chemical changes which they occa- 

 sion in the living tissues, as in any degree different from those which they would 

 effect on substances of the same composition not endowed with life. A still 

 more remarkable influence is exerted by those " ferments" or Septic poisons, 

 which have a special power of exciting and promoting decomposition in the 

 components of the tissues ( 19) ; for of these, the introduction of an extremely 

 minute quantity into the organism is sufficient to pervert or even to destroy its 

 entire vital activity. Those of the less potent kind appear to act, not by at 

 once checking the nutritive operations, but by lowering or degrading them; 

 accelerating the stage of degeneration in the tissues which are already in a 

 state of vital activity, and preventing the newly-originating tissues from attain- 

 ing their normal perfection either of structure or of action, so that the degene- 

 rative stage in them also is more speedily induced. But there are some which 

 appear to be capable of putting an almost immediate stop to all the vital opera- 

 tions of the system, in virtue of the changes of composition which they effect ; 

 and here too we observe, that the poisons which are most powerfully destructive 

 of life, are those which induce the most rapid degradation of the organic com- 

 ponents of the tissues to the state of inorganic compounds, as is shown by the 

 very speedy decay of the bodies of those who have died from the bites of ser- 

 pents, malignant fevers, &c., a state of putrescence manifesting itself in many 

 instances even before life is extinct. 



116. Thus, then, we may state it as a general fact, that, so far from the Living 

 Organism having the power of resisting the operation of Chemical and Physical 

 Agencies, it is completely amenable to them; but that certain of them exert 

 their influence upon it in a mode very different from that in which they act on 

 dead matter, affording, in fact, the material and dynamical conditions requisite 



' "Prin. of Phys., Gen. and Comp.," gg 107-112, Am. Ed. 



2 This condition will be shown hereafter (CHAP. xi. SECT. 3) to involve a lowering of the 

 vital powers of the solid tissues which it affects. 



