This leads us to consider some of the elements, conditions and forces which give character to the organization. External circumstances supply necessary conditions to inward activity, for without air, food, or sunlight all living animals would perish. Everywhere, life is dependent upon conditions and circumstances; it is not self-generating. But the conditions of reproduction are very complex. External forces are transformed, and, in turn, become vital or formative powers. Development is a transmutation of physical and chemical forces into vital energy. Although unable to compute the ultimate factors of life, yet we may illustrate their reproductive possibilities and results by comparing them with those of a lower order.
Animal structures are mainly composed of four elements: oxygen, hydrogen, nitrogen and carbon. Other constituents, such as phosphorus, sulphur, potassium, sodium, calcium, magnesium, and iron, enter into their composition, but are found in much smaller quantities. From these elements is fabricated an organism which manifests peculiar properties and marvelous functions. If the proportion of these chemical elements be varied, the organic compound will be changed, or, the proportions remaining the same, if the grouping of the elements be altered, different compounds will be produced, showing that the properties of organized substances depend upon the molecular constitution of matter.
Rising in the scale of organization, we observe that every variation of the physical and chemical processes implies a corresponding modification of the vital. This is verified by the peculiarities of the several races of mankind. Individual differences are likewise modifications of these processes. Dynamical or vital differentiation depends upon these modifications for the display of vital energy, and is always associated with molecular changes. But it should be borne in mind that an effect may not resemble its cause in properties, and the qualities of a chemical compound may be quite different from those of its individual constituents. Organic matter, although more complex, may exhibit properties, both like and unlike its constituent elements. Within certain boundaries, the elements seek to satisfy their affinities. We discover that there are limits between the genera of animals, as well as the races of mankind. Not less really, though perhaps not as absolutely, are there individual precincts within the sphere of the human temperaments, which cannot be passed.
If we cannot satisfactorily explain, we can at least discover a reason for temperamental limitation. It is not designed to circumscribe healthful reproduction, but to serve as an effectual hindrance to abnormal deviations. We may state our belief in more positive terms: that the temperamental variations are essential to genesis and fertility, and indispensable to health and normal development.
Every individual is susceptible to impressions which dispose to action. Impressions which excite or increase this disposition, are called stimuli. Vital change implies the existence of stimuli and susceptibility to stimulation. The stimulus may not be furnished because the conditions on which it depends are wanting; again, susceptibility may exist at one time and not at another. Stimuli and susceptibility may be present in different degrees, but for the purpose of healthful reproduction they must not be impaired. No single class of foods, albuminous, starchy, saccharine, or mineral, is sufficient for the nutrition of the body, but the food must contain substances belonging to each of the different classes. If an animal be fed exclusively upon albumen, though this substance constitutes the largest part of the bodily mass, exhaustion will rapidly follow, since the food does not contain all the essential, nutritive elements. Again, when the solids of the body have been wasted, they lose their susceptibility to stimuli, and the food does no good. Thus patients become emaciated during acute attacks of disease, upon the cessation of which they are too feeble to recover, simply because they have lost the power to digest and assimilate their food.
In inanimate bodies, as in crystals, forces come to rest, but the very idea of life implies action and continual change. Hence diversity of constitutions and different temperaments are essential in order that marriage may result in the reproduction of vigorous beings.
VITAL AND NON-VITAL TEMPERAMENTS.
In the preceding chapter, we attempted to illustrate the unique blending of mind and body by means of the nervous system, and we now propose to exemplify the physical conditions of the organism by certain correspondences, observed in the development and conditions of that system. If nature answer to mind in physical correspondences, she will observe the same regularity in physical development. The simplest classification of the temperaments is represented in Fig. 78. Not only is mental activity dependent upon a vital activity in the brain, but the development of the cerebrum is dependent upon the supply of blood. The growth of the intellect requires the same conditions that aided in the development of Vulcan's right arm: waste and supply; disintegration and reparation of tissue. Our modern iron forges produce many an artisan whose great right arm proclaims him to be a son of power as well as of fire. Thus the fervid intellect, while forging out its thoughts, increases in size and strength. The difference between the development of the two is this; that the exercise of the blacksmith's right arm quickens the activities of all the bodily functions, whereas the employment of the intellect does not offer any healthy equivalent. Physical exercise is a hygienic demand, but intellectual employment exerts no salutary influence on the body, while it is constantly expending the nutritive energies of the blood. The emotions, likewise, make exhaustive draughts upon nutrition to supply the waste of brain substance, just as certainly as physical labor causes muscular change, and demands reparation. One expends cerebral, the other, muscular substance. The one is healthful in its general tendencies, the other, comparatively wasteful and destructive.
| { | DISINTEGRATING, | |
| The intellectual faculties are | EXPENDING, | |
| DERIVING. | ||
| { | ENGROSSING, | |
| The emotive faculties are | EXHAUSTING, | |
| DEVITALIZING. |