CONDITIONS OF VITAL ACTIONS. 217 



acquaintance with its history would detect its progressive though tardy exten- 

 sion, and would ascertain that it multiplies its race by an humble yet effectual 

 process of fructification. Or the change may be rather evidenced, by the 

 performance of some kind of movement, for which the ordinary physical 

 laws of matter will not account ; yet, for the detection of this, a close and 

 careful scrutiny will be frequently required. Thus the Oyster that is lying 

 motionless in its massive bed, or the Ascidia that clusters upon the faces of 

 sea-beaten rocks, may seem totally destitute of activity ; yet it would be found 

 upon close examination, that their internal surfaces are covered with cilia 

 which are in continual vibration, that by this means water is drawn into 

 the stomach and caused to traverse the respiratory organs, yielding to the 

 former the animalcules it may contain, and to the latter the oxygen dissolved 

 in it, that the food thus introduced into the stomach undergoes digestion, and 

 is converted into materials adapted to nourish the body, which are then con- 

 veyed to its different parts by a circulating apparatus, that in due time em- 

 bryos are produced, which are endowed with powers of active motion, and 

 which swim forth from within the parent-envelopes and locate themselves 

 elsewhere, and that, apathetic as these creatures may seem, they may be 

 excited by certain kinds of stimuli to movements which seem to evince sen- 

 sation ; the Oyster closing its shell, and the Ascidia contracting its muscular 

 tunic, when it receives any kind of mechanical irritation ; and the former, 

 whilst lying undisturbed in its native haunts, drawing together its valves, if a 

 shadow passes between itself and the sun. From what has been already 

 stated, regarding the nature of the actions of the Nervous and Muscular sys- 

 tems, by which the movements of Animals are chiefly effected, it would ap- 

 pear that these, in common with the Vegetative functions, involve a chemical 

 alteration in the structure performing them ; so that it may be stated as a 

 general proposition, that a change in Chemical composition is an essential 

 condition of every Vital phenomenon. 



255. If change be essential to our idea of Life, it may be asked, what is 

 the condition of a seed, which may remain unaltered during a period of many 

 centuries ; vegetating at last, when placed in favourable circumstances, as 

 if it had only ripened the year before. Such a seed is not alive; for it is not 

 performing any vital operations. But it is not dead, for it has undergone no 

 decay ; and it is still capable of being aroused into active life, when the proper 

 stimuli are applied. And the most correct designation of its state seems to 

 be that of dormant vitality. The condition of an animal reduced to a state of 

 complete torpidity and inaction, is precisely similar ; into such a condition, 

 the Frog may be brought by cold, and the Wheel-Animalcule by deprivation 

 of moisture. And the condition of a Human being, during sleep, is precisely 

 similar, so far as his psychical powers are concerned ; he is not then a feel- 

 ing, thinking Man ; but he is capable of feeling and thinking, when his 

 brain is restored to a state of activity, and its powers are called into operation 

 by the impressions of external objects. 



256. There can be no doubt whatever, that, of the many changes which 

 take place during the life, or state of vital activity, of an Organised being, 

 and which intervene between its first development and its final decay, a large 

 proportion are effected by the direct agency of those forces which operate in 

 the Inorganic world; and there is no necessity whatever for the supposition, 

 that these forces have any other operation in the living body, than they would 

 have out of it under similar circumstances. But after every possible allowance 

 has been made for the operation of Physical and Chemical forces in the living 

 Organism, there still remain a large number of phenomena, which cannot be 

 in the least explained by them ; and which we can only investigate with suc- 

 cess, when we regard them as resulting from the agency of forces, as distinct 



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