OF CELLS AND CELL-LIFE. 135 



tion of the tissues in warin-blooded animals, seems to lie in the uniformity of 

 the temperature at which they are kept, which uniformity tends to produce a 

 determinate regularity in the rate of their vital activity ( 127). As already 

 remarked, the very influences which call into action the vital properties of a 

 living tissue, tend to produce its decay, when it no longer possesses the faculty 

 of turning them (so to speak) to this account ; and thus it is that, in warm- 

 blooded animals, the cessation of those changes in which life consists, immedi- 

 ately leaves the way clear for that disintegration which is effected by Chemical 

 forces, and this the more actively as the temperature is higher. The only tis- 

 sues, indeed, that can resist the operation of these forces are such as, in virtue 

 of their peculiar composition, are not readily affected by them. Thus we find 

 that bones, teeth, hairs, &c., may have their existence almost indefinitely pro- 

 longed, without any sensible degeneration, after the complete cessation of all 

 vital changes in their substance ; since that very consolidation of these tissues, 

 which put them out of the pale of active life, at the same time rendered them 

 less subject than before to the degrading influence of Chemical agencies. Even 

 the softest and most decomposable of the tissues may be preserved from decay, 

 provided that they are either kept at a sufficiently low temperature, or are en- 

 tirely secluded from oxygen, or are completely deprived of their moisture ; either 

 of which conditions is incompatible with the persistence of vital activity. And 

 thus it happens that not only the seeds of Plants, but many Animal organisms 

 of a high degree of development, may be kept in a dormant condition for an. 

 unlimited period, by the reduction of their temperature or the withdrawal of 

 the liquid components of their structure; ready for a renewal of their vital ac- 

 tivity, whenever the deficient conditions may be supplied. 1 



115. The different behavior (to use a term now naturalized in Chemical 

 Science) of the living and of the dead organism under the same conditions, is 

 commonly accounted for by the supposition, that the Vital force, so long as it 

 endures, antagonizes the operation of the Physical and Chemical agencies, which 

 are constantly tending to the disintegration of the living structure ; and that, 

 so soon as the former is extinct, the latter can exert their influence without 

 restraint or opposition. But against this doctrine, several cogent objections may 

 be adduced. For in the first place, the conditions most favourable to the decay 

 of the organism after its death, are those which are not only most favorable, but 

 are absolutely essential, to its life, whilst it retains its vital properties ; the 

 presence of Water being requisite for all the transformations which the nutrient 

 materials undergo, as well as for the very construction of a cell ; the presence 

 of Oxygen being necessary for the greater number, if not for the whole, of the 

 chemical actions which the life of the cell involves ; and the dynamical agency 

 of Heat being so completely indispensable, that the amount of Vital Action put 

 forth may be almost considered as the definite equivalent of the amount of this 

 power that is in operation. 3 But if more than a certain measure of these powers 

 should be exerted, the effect is not beneficial, but injurious, to the living organ- 

 ism, which is then acted on as if it were composed of dead matter. Thus we 

 see that whilst to every living being there is a certain range of temperature, 

 more or less limited, within which its vital activity is normally exercised, any 

 considerable elevation above that standard occasions a perversion of that activity, 

 which tends to its destruction ; and a heat sufficient for the decomposition of 

 its organic constituents is not less effectual in producing this change on the liv- 

 ing body, than it is on the dead. So, whilst the respiration of atmospheric air 

 is necessary for almost every manifestation of life, the introduction of undiluted 

 oxygen into the system is speedily fatal, apparently through the violence of the 



' See "Prin. of Phys., Gen. and Comp.," CHAP. in. SECT. 4, Am. Ed. 



2 Op. Cit., CHAP. III. SECT. 3. 



