Acclimatization

“ Vigorous, healthy persons of moderately spare frame, with sound viscera, and who are of temperate habits, if the atmosphere be pure and moderately dry, can sustain a great amount of heat. Acclimatization has also some influence in conferring toleration. ”

“ The subject of acclimatization is very little understood, and some writers have even denied that it can ever take place. It is often confounded with domestication or with naturalization; but these are both very different phenomena. A domesticated animal or a cultivated plant need not necessarily be acclimatized; that is, it need not be capable of enduring the severity of the seasons without protection. The canary bird is domesticated but not acclimatized, and many of our most extensively cultivated plants are in the same category. ”

“ The increment of length divided by the increment of time gives the absolute rate of growth at any part of the curve. As long as the growth is uniform, so long the slope of the curve remains constant. If a stimulating agency enhances the rate of growth, there is an immediate upward flexure in the curve; a depressing agent, on the other hand, lessens the slope of the curve.
I shall now give a few typical examples of the employment of the Crescograph for in­ves­ti­ga­tions on growth: the first example I shall take is the demonstration of the influence of variation of temperature. ”

“ It is not necessary for us to pursue this subject much further, for it is sufficiently clear that the normal “curve of growth” of an organism, in all its general features, very closely resembles the velocity-curve of chemical autocatalysis. We see in it the first and most typical phase of greater and greater acceleration; this is followed by a phase in which limiting conditions (whose details are practically unknown) lead to a falling off of the former acceleration; and in most cases we come at length to a third phase, in which retardation of growth is succeeded by actual diminution of mass. ”

“ Besides the quality, the direction and the intensity of every alteration in vital conditions, an equally important factor is the duration of the alteration. The time relations, under which a deviation of the external vital conditions takes place, present immense and manifold variations in nature. In many cases the change is very complicated, as for instance, the alteration of the static pressure or the temperature under the influence of air or water currents, the osmotic pressure or chemical factors in diffusion currents, and the light intensity produced by the movement of clouds. ”

“ Again, as I have shown in a series of communications, a similar phenomenon is displayed in growth which initially undergoes acceleration and therefore slows down. Indeed acceleration and slowing may alternate a number of times in the same organism producing what I have termed 'growth cycles.' This type of phenomenon would appear very generally displayed in the performance of life-activities, and indeed I am inclined to think with Loeb that the self conserving character of the life-process will ultimately find its solution in the study of phenomena of this description. ”

“ The ever present tendency of geotropic movement is opposed or helped by the physio­logic­al reaction induced by rise and fall of temperature respectively. The state of equilibrium is never permanent, but the dynamic balance is being constantly readjusted under changing conditions of the environment. ”

“ All winds are caused by the disturbances of indifferent equilibrium, and the motion of the air is to restore equilibrium.
2. These disturbances are caused through overheating of the layers of air near the surface of the earth by insolation, through unsymmetrical cooling of the higher layers by radiation, and through the heaping up of air masses caused by obstructions.
3. The disturbances are adjusted by ascending currents, wherein the particular species of acceleration occurs in which the increase of velocity is proportioned to the diminution of pressure. ”

“ TROPIC EQUILIBRIUM UNDER VARYING INTENSITIES OF STIMULUS.
The following experiment will show that the position of tropic equilibrium is not fixed but subject to variation under changes of effective stimulation.
Fig. 185.—Effect of variation of intensity of light on phototropic equilibrium. Increase of intensity of light from L to L' produces an increased positive curvature and a new state of balance. Diminished intensity of light l brings about a new balance at a lower level. The cessation of light (l within a circle) restores the normal position of the organ. ”

“ In specific gravity the alteration, though not very marked, is still in the same direction. Development being habitually accompanied by a relative decrease in the quantity of water and an increase in the quantity of constituents that are heavier than water, there results a small augmentation of relative weight. In power of maintaining a temperature above that of surrounding things, the differentiation from the environment that accompanies development is marked. All ova are absolutely dependent for their heat on external sources. ”

“ Response to feeble stimulus by acceleration of growth; (b) response to strong stimulus by retardation of growth; (c) response to medium stimulation—retardation followed by recovery. Down-curve represents acceleration, and up-curve retardation of growth (seedling of wheat) . range of the plant is inconceivably greater than ours; it not only perceives, but also responds to different rays of the vast ethereal spectrum. ”

“ A very troublesome complication of pulsations in growth, arises at high temperatures, which render further record extremely difficult. Growth is undoubtedly a pulsatory phenomenon; but under favourable circumstances, these merge practically into a continuous average rate of elongation. At a high temperature the effect of certain disturbing factors comes into prominence. ”

“ The system suffers less when the change of temperature is gradual. The change in the production of heat, as well as in the evaporation of fluids from the system, is gradual when not influenced by foreign causes. This gradual change is known under the name acclimation. By this means the body is enabled to endure tropical heat and polar cold. Owing to this gradual adaptation of the system to different temperatures, we can bear a greater degree of heat in the summer between the tropics, than in the winter under the polar circles. ”

“ In particular we should like to know the meaning of that point of inflection, or abrupt change from an increasing to a decreasing velocity of growth which all our curves, and especially our acceleration curves, demonstrate the existence of, provided only that they include the initial stages of the whole phenomenon: just as we should also like to have a full physical or physiological explanation of the gradually diminishing velocity of growth which follows, and which (though subject to temporary interruption or abeyance) is on the whole char­ac­ter­is­tic of growth in all cases whatsoever. ”

“ Equilibration is the final result of these trans­for­ma­tions which an evolving aggregate undergoes. The changes go on until there is reached an equilibrium between the forces which all parts of the aggregate are exposed to and the forces these parts oppose to them. Equilibration may pass through a transition stage of balanced motions (as in a planetary system) or of {142} balanced functions (as in a living body) on the way to ultimate equilibrium; but the state of rest in inorganic bodies, or death in organic bodies, is the necessary limit of the changes constituting evolution. ”

“ Yet the ideal or abstract moving equilibrium, by whose aid we are endeavouring to understand the actions of organisms, is derived from the consideration of the solar system as a moving equilibrium. But reducing the problem from the abstract to the concrete study of an organism, we have to ask what place consciousness holds in a moving equilibrium of oxygen, nitrogen, carbon, hydrogen, etc., in relation with an environment of heat, light, etc. ”

“ Acclimatisation.—Habit is hereditary with plants, as in the period of flowering, in the amount of rain requisite for seeds to germinate, in the time of sleep, &c., and this leads me to say a few words on acclimatisation. As it is extremely common for species of the same genus to inhabit very hot and very cold countries, and as I believe that all the species of the same genus have descended from a single parent, if this view be correct, acclimatisation must be readily effected during long-continued descent. ”

“ Before inquiring in what ways the rapidities of increase are adjusted to the requirements, both temporary and permanent, it will be needful to look at the factors. Let us set down first those which belong to the environment, and then those which belong to the organism.
§ 316. Every living aggregate being one of which the inner actions are adjusted to balance outer actions, it follows that the maintenance of its moving equilibrium depends on its exposure to the right amounts of these actions. ”

“ The higher the temperature, and the farther it is removed from the equilibrium point (transition point) , the greater is the velocity of change. Above the transition point, these two factors act in the same direction, and the velocity of transformation will therefore go on increasing indefinitely the higher the temperature is raised. Below the transition point, however, the two factors act in opposite directions, and the more the temperature is lowered, the more is the effect of removal from the equilibrium point counteracted. ”

“ For a great part of the difference, in regard to rate of growth, between one individual and another is a difference of phase,—a difference in the epochs of acceleration and retardation, and finally in the epoch when growth comes to an end. And it follows that the variability of rate will be more and more marked, as we approach and reach the period when some individuals still continue, and others have already ceased, to grow. ”

“ In statical equilibrium, any downward movement of an air mass would simply be accompanied by the natural rise in temperature corresponding to the transformation of its energy of position, but in this condition of stable equilibrium any motion downwards must involve, not only this natural temperature rise, but also a return, either in whole or in part, of the energy absorbed from the aqueous vapour. ”

“ Geddes and Thomson, _The Evolution of Sex_, p. 220.
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out-flowing processes, the normal activity of growth may be
restored. Till this moment nothing would be gained by any of
these changes. One or other of them is now conducive to
progressive absorption of energy by the organism, and one or
other occurs, most generally the best of them, subdivision. Two
units now exist; the total mass immediately on division is
unaltered, but paths for the more abundant absorption of energy
are laid open. ”

“ Looked at from above, the opening outwards during rise of temperature is a movement downwards, and therefore belongs to the negative type. In such cases the changed rate of growth by variation of temperature is the most important factor in the movement. It may be asked whether all thermonastic movements must necessarily belong to the negative type, where rise of temperature is attended by a movement downwards. ”

“ Further, I shall suppose that in this world all bodies have the same co-efficient of dilatation, so that the linear dilatation of any body is proportional to its absolute temperature. Finally, I shall assume that a body transported from one point to another of different temperature is instantaneously in thermal equilibrium with its new environment. ”

“ As all the more comprehensive groups present this relation to each other, we are compelled to believe that acceleration has been the principle of their successive evolution during the long ages of geologic time. ”

“ In short, the char­ac­ter­is­tic form of the curve of growth in length (or any other linear dimension) is a phenomenon which we are at present unable to explain, but which presents us with a definite and attractive problem for future solution. It would seem evident that the abrupt change in velocity must be due, either to a change in that pressure outwards from within, by which the “forces of growth” make themselves manifest, or to a change in the resistances against which they act, that is to say the tension of the surface ”

“ They arise from any disturbance by temperature, motion, pressure, &c. of the equilibrium of the atmosphere, and are the efforts of nature to restore the balance. Their office in the economy of nature is to carry heat and moisture from one tract to another, and they are the great agents in the distribution of temperature and the changes of weather. ”

“ This gives a horizontal record; an acceleration of growth above the normal is, in the [Pg 422] following records, represented by a down curve, and a retardation by an up-curve.
Effect of feeble stimulus: Experiment 161.—I first studied the effect of feeble stimulus. This was secured by decreasing the energy of sparks of the radiator. The response was an acceleration of rate of growth as seen in figure 156a. The analogy of this with the accelerating effect of sub-minimal intensity of light (p. 224) is very remarkable. ”

“ Cope founded his belief, that the adult characteristics were also the result of acceleration, if I rightly remember it, mainly upon the class of facts spoken of above in man where a sudden change into two organs may produce entirely new and unexpected differences in the whole organisation, and upon the changes which acceleration appeared to produce in the development of each succeeding species. ”

“ After-oscillation.—In the case of the sensitive silver cell, we have seen (fig. 105) , when it has been subjected for some time to strong light, that the current of response attains a maximum, and that on the stoppage of the stimulus there is an immediate rebound towards recovery. In this rebound there may be an over-shooting of the equilibrium position, and an after-oscillation is thus produced. ”