Front Page Titles (by Subject) CHAPTER VI.: THE CORRESPONDENCE AS DIRECT AND HOMOGENEOUS. - The Principles of Psychology
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CHAPTER VI.: THE CORRESPONDENCE AS DIRECT AND HOMOGENEOUS. - Herbert Spencer, The Principles of Psychology 
The Principles of Psychology (London: Longman, Brown, Green and Longmans, 1855).
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THE CORRESPONDENCE AS DIRECT AND HOMOGENEOUS.
§ 127. As the highest life is found in the most complicated environments, so, conversely, the lowest life is found in environments of unusual simplicity. Most environments present both coexistences and sequences; but there are some that during a limited period, present coexistences only; and in these, during this limited period, occur the organic forms to which, by common consent, is assigned the lowest place, both in respect of structure and vital properties. Of those classed with the vegetable kingdom, may be instanced the yeast-plant, and the Protococcus nivalis (red snow fungus). Of those held to be of animal nature, the Gregarina, and the parasitic cell which causes smallpox, may be taken as samples. The life of each of these organisms consists, almost wholly, of a few cotemporaneous processes in correspondence with the coexistent properties of the medium which surrounds it. The yeast-plant has for its habitat, a fluid consisting of water holding in solution certain hydrocarbons, some nitrogenous matter, oxygen, and probably other elements in minor proportions. That it may flourish, the temperature must be maintained within certain limits, and light must be excluded. These conditions being fulfilled, the yeast-plant displays what we call vital changes, in correspondence with the chemical changes of the elements bathing its surface—the cell grows; the fluid ferments: and while the fluid continues to supply the needful materials under the needful conditions, the cell continues to display the same phenomena. But let the temperature be considerably raised, or some of the ingredients exhausted, and the respective actions cease. The life, limited in length to the brief period during which the environment remains practically uniform, exhibits no successive changes such as those by which a shrub responds to the alternations of day and night, of the seasons, of the weather. Excluding those modifications of form and size which are the necessary concomitants of continued assimilation, the only successive changes which the yeast-plant displays, in common with the higher plants, are those which result in the formation of spores. Dependent as they possibly are upon those alterations of the environment which continued fermentation produces—perhaps partly determined by the diminishing quantities of the materials needful for growth—these generative actions may be regarded as successive changes corresponding with successive changes in the environment; and most likely there is no organism but what, in addition to the simultaneous processes taking place in it, undergoes a serial process of this character. Evidently, however, the two orders of change, answering in this case to the two all-essential functions of assimilation and reproduction, exist under their simplest forms, in correspondence with the simplest relations in the environment; and ending as they do with that new state of the environment soon arising, the life is as short as it is incomplex.
It is needless to present in detail each of the other cases referred to. Substantially, they are severally of the same nature as the foregoing one. The Protococcus nivalis exists only in snow—a medium simple and constant in chemical character; confined in its variations of temperature; and which only under still more special conditions than those common to it, contains this microscopic fungus. Propagating itself over large tracts in the arctic regions in the course of a single night, during which the surrounding circumstances must remain almost uniform, this minute organism exhibits vital processes corresponding only to the surrounding coexistences; and can undergo scarcely any changes corresponding to surrounding sequences. To a new state in its medium, it does not adapt itself but dies: the snow melts and it disappears. Similarly with the Gregarina—a single-celled creature which inhabits the intestines of certain insects; which is bathed by the nutritive fluid it assimilates; which is kept at a tolerably constant temperature; and which can continue to exist no longer than its special environment exists. And so too with the organic monads which constitute the virus of smallpox—monads which live in the blood; which multiply at the expense of certain of its constituents; which are preserved by it in conditions liable to little variation; and which cease to exist when their habitat has undergone that slight modification which the disease causes in the constitution. In all these cases the peculiarities to be noted are:—first, that the actions in the organism are in immediate dependence upon the affinities of the elements touching it on all sides; and second, that the internal processes of change proceed uniformly, or nearly so, because, during the brief time that the life lasts, the external relations remain uniform, or nearly so. The correspondence is at once direct and homogeneous. The disintegrating matter and the matter to be integrated, being everywhere diffused through the environment, it results that all the agents to which the vital changes stand related, are not only in contact with the organism, but continuously in contact with it. And hence the reason why there need neither those motions nor locomotions, which, where they are found, involve more or less heterogeneity in the correspondence.
§ 128. In strictness, no other forms of life than those of the kind just described, can be said to exhibit a correspondence at once direct and homogeneous. But the transition to higher forms is so gradual, that in making groups, it is impossible to avoid incongruities; and on the whole, it seems best to notice here a class of organisms, which, while they exhibit motion, either positive or relative, do so with comparative uniformity—a uniformity which implies that the correspondence is almost as homogeneous as in the cases above given. The ciliated spores of the algæ; the simplest of the ciliated animalcules; the most regular of the compound ciliated organisms, as the Volvox globator; together with the sponges and their allies; may be instanced as displaying this order of life.
Water, either fresh or salt, being in all these cases the medium inhabited, the general fact to be observed, is, that the incipient heterogeneity in the vital actions, is in correspondence with the incipient heterogeneity of the environment. Though, from a human point of view, the fluids in which the yeast-plant and the Gregarina live, are far more heterogeneous than the water, either of the sea or of a pond; yet, relatively to these contained organisms, they are less so. For whilst on the one hand, every portion of the wort bathing the cell-wall of the yeastplant, and every portion of the nutritive emulsion surrounding the Gregarina, presents the matter to be assimilated; on the other hand, every portion of the water in which a protozoon swims, though it presents oxygen, does not always present nutriment. In a concentrated form as the food of the first is, and in a dispersed form as is that of the last; it is clear that the external relations must be more homogeneous to the one than to the other. And manifestly, an organism whose medium is unceasingly disintegrating it, but is not unceasingly supplying it with integrable matter, but only presents scattered atoms of such integrable matter, must either traverse its medium with such velocity as shall bring it in contact with the requisite quantity of integrable matter, or must cause the medium to move past it with the like velocity—must either have a positive motion, as the infusory animalcule, or a relative motion, like that of the sponge towards the current of seawater it draws in and expels. Thus then, the addition of mechanical change to the changes displayed by motionless organisms, is the addition of new internal relations in correspondence with new external relations.
Further, it is to be remarked, that the processes by which the movement is effected, are themselves in direct and almost homogeneous correspondence with certain almost ever-present properties of the environment. The fact that the ciliary action of fresh-water creatures ceases when they are put into sea water, and that of sea-water creatures when they are put into fresh water; joined with the fact that when the creatures displaying it have been killed, the ciliary action on the uninjured parts, and even on parts that have been cut off, continues for a long time; and joined with the further fact, discovered by Virchow, that ciliary motion, which has ceased, may be reproduced by a solution of caustic potash; suffice to show, that the motion of these microscopic hairs is caused by the immediate contact of some matter or agent in the environment—consists of a succession of minute internal changes, in correspondence with those minute recurring actions of the medium which the waving of the cilia themselves involve. And the occasional suspensions and reversals of the motion, commonly so sustained, may possibly result from local deficiencies in the medium, of those materials or conditions that determine it; in which case, this slight heterogeneity in the mechanical changes, is in correspondence with a slight heterogeneity in the environment.
Other tribes of marine creatures, as the Thalassicola, display types of correspondence somewhat unlike the foregoing in character, though differing little in degree. But it is unnecessary to do more than indicate them.