LIFE. 



157 



state of torpidity by cold, some vital action 

 usually continues ; and such cases cannot 

 therefore be adduced under the present head. 

 But instances are by no means rare in which 

 the whole body has been frozen, and vital action 

 has of course been completely suspended, yet 

 without the destruction of the power of renew- 

 ing them under more favourable circumstances. 

 Lister first noticed that he had found caterpil- 

 lars so frozen, lhat when dropped into a glass 

 they chinked like stones, but nevertheless re- 

 vived ; and this statement has been confirmed 

 by Bonnet and others. The Papilla Brassicee 

 lias been produced from a larva which had been 

 exposed to a frost of Fahr., and which had 

 become a lump of ice. Fishes are occasion- 

 ally found imbedded in the ice of arctic seas; 

 and some of these revive when thawed. This 

 tenacity of life appears greater, however, in the 

 species which are confined to shallow lakes or 

 ponds, and which have not the power, there- 

 fore, of escaping from the effects of cold. This 

 is perhaps the proper place to mention those 

 undoubted cases in which insects have been 

 apparently killed by immersion in water or 

 spirit, continued for a long period, and have 

 yet revived on exposure to the air and sun. 



Without multiplying facts, then, it may be 

 safely affirmed that many organised beings 

 may retain their vital properties, in some in- 

 stances to an unlimited duration, while all vital 

 activity or life is completely suspended, through 

 the absence of the stimuli necessary to main- 

 tain it ; and that this preservation of vitality 

 bears so close a relation to the resistance offered, 

 by the structure and composition of the sub- 

 stance possessing it, to the influence of disin- 

 tegrating agents, that it may reasonably be 

 considered as a result of the maintenance of 

 its normal constitution. The physiologist is 

 not yet in a condition to explain those diffe- 

 rences in structure and composition which 

 enable some organisms to offer a much greater re- 

 sistance to such injurious influences than others ; 

 but he considers himself entitled to assume that 

 such exist in all, since there are many instances 

 in which he is able to detect them. 



Suspension of vital action under other cir- 

 cumstances. We have next to consider those 

 cases in which vitality is rendered for a time 

 dormant, by causes originating in the system 

 itself, rather than by the %vithdrawal of external 

 stimuli. Under this head we may place all 

 those phenomena to which the name of hyber- 

 nation is usually given ; but which, as will 

 presently be seen, cannot be appropriately de- 

 signated by that term. The greater number of 

 plants indigenous to temperate climates un- 

 dergo an annual series of phases, in which 

 their vegetative processes exhibit every grada- 

 tion from a torpor apparently complete to the 

 most surprising activity. In many, indeed, 

 this series of phases constitutes the whole of 

 life ; the individual ceasing to exist as soon as 

 it has been once performed, and a new genera- 

 tion called into existence. In many more, a 

 total suspension of activity appears to take 

 place, as may be observed in plants whose 

 stems die annually, whilst the roots retain their 



vitality. This condition exactly resembles that 

 of certain animals which pass the winter in a 

 state of profound torpor. In those, however, 

 whose stems are woody and persistent, vital 

 action does not seem to be completely checked 

 even by a frosty atmosphere ; as late experi- 

 ments show that a movement of sap takes 

 place, though to a trifling degree, in the depth 

 of winter. And, lastly, in evergreen plants, 

 these changes of condition are less complete ; 

 the activity of the vegetative processes being 

 diminished by the partial withdrawal of their 

 appropriate stimuli, but not being altogether 

 suspended. Now although it is unquestion- 

 able that this series of changes is greatly influ- 

 enced by the successive alterations in the ex- 

 ternal conditions of the beings, which the 

 revolution of the seasons induces, it does not 

 admit of doubt that it is originally dependent 

 on the peculiar constitution of the organism, 

 by which a periodical diminution of its activity 

 is occasioned. For nothing will prevent a 

 plant from shedding its leaves nearly at its 

 usual time ; and although by artificial heat, or 

 by removal to a warmer climate, a new crop may 

 be brought out within a short interval, this can 

 only be effected by keeping in a state of activity 

 the processes which ought to be at rest, so that 

 an injurious influence is exerted on the general 

 system like that which results from artificially- 

 prolonged watchfulness in animals. When a 

 plant is reduced, by the periodical decay of its 

 stem and leaves, to the state of a bulb or root, 

 it seems almost to revert to that remarkable 

 condition already described as peculiar to seeds ; 

 the vitality of the structure being capable of 

 remaining dormant for a considerable time, and 

 of being then aroused into full activity by the 

 appropriate stimuli. We are not aware of any 

 authentic facts which fix the limit to the dura- 

 tion of this condition. Instances have been 

 related of the growth of bulbs unrolled from 

 the envelopes of Egyptian mummies ; but 

 there is reason to believe that deception has 

 been practised on this point upon the too-ready 

 credulity of travellers. However, there can be 

 no doubt that, under favourable circumstances, 

 bulbs and roots may be preserved for many years ; 

 the conditions necessary for thisobject being such 

 as neither excite the vitality of the structure to 

 action, nor occasion the disintegration of the 

 latter and the consequent loss of its properties. 



The animal kingdom presents us with condi- 

 tions very analogous to those just alluded to. 

 In a large proportion of those inhabiting tem- 

 perate climates, there is a periodic diminution 

 of vital activity during the colder part of the 

 year; but this, in the higher tribes at least, 

 scarcely amounts to an absolute suspension, 

 since the circulation, and the functions of nu- 

 trition and secretion which depend on it, are 

 carried on, though feebly. (See HYBERNATION.) 

 It is easy to understand why this must be the 

 case. The softer portions of the animal frame, 

 which are most concerned in the processes of 

 organic life, are not periodically cast off and 

 renewed like the corresponding parts of plants ; 

 and, if their integrity were not maintained by 

 the circulation of nutritious fluid during their 



