a. 
“y 
LIFE. 
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 
Tg te the destruction of the power of renew- 
“ing them under more favourable circumstances. 
- Lister first noticed that he had found caterpil- 
lars so frozen, that when dropped into a glass 
they chinked like stones, but nevertheless re- 
_vived ; and this statement has been confirmed 
_ by Bonnet and others. The Papilio Brassice 
has been produced from a larva which had been 
" exposed to a frost of 0° 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 
age 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 
ently killed by immersion in water or 
irit, continued for along period, and have 
_ yet revived on exposure to the air and sun. 
_ Without multiplying facts, then, it may be 
‘atl 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 
absence of the stimuli necessary to main- 
in it; and that this preservation of vitality 
so close a relation to the resistance offered, 
y the structure and composition of the sub- 
“Stance possessing it, to the influence of disin- 
tegrating agents, that it may reasonably be 
msidered as a result of the maintenance of 
its normal constitution. The physiologist is 
‘hot yet in a condition to explain those diffe- 
a in strueture and composition which 
-enablesome 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 
eases in which vitality is rendered for a time 
dormant, by causes originating in the system 
itself, rather than by the withdrawal 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 
hog indigenous to temperate climates un- 
ergo 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, 
is 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 
157 
vitality. This condition exactly resembles that 
of certain animals which pass the winter ina 
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 itjs 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 toa 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. Whena 
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, 
bulbsand roots may be preserved for many years ; 
the conditions necessary for this object 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 
