apparatus, an ante-stomach whose history of evolution, covering thousands of years, distinctly shows the increasing demands for digestibility and relish, the need to diminish the work of the teeth and to ease the process of mastication. The starting-point is here the function of taking and assimilating food.
In this sense it is not only permissible but necessary to speak of an evolution of physiological functions. No organic structure develops without having an activity, a necessity, to intensify this activity for its cause. The cause of this increase in activity or differentiation is simply functional evolution. It is the principle of all organic growth, of all morphological evolution, and, wherever it decreases or ceases, the latter at once retrogrades. Without function, no organic formation; increase of function, organic differentiation; cessation of function, organic retrogression.
In applying this principle to the physical and mental activities of the healthy and the sick human being, physiological inquiry must of necessity be carried on in two directions. Since it is necessary to know not only the nature of functions, but also how they have evolved, the evolving living body, the embryo, must be physiologically examined. That is one direction. To compare the complex functions of man, the most complex of all beings, with the less perfected functions of animals—and of plants too—is the other task. Physiology must be comparative only, said, in 1826, Johannes Müller. The genetic and the comparative science of functions go together. Both, as yet incipient, must by-and-by become the basis of the biology of the future.
Each single function of man must step by step be followed back to its first manifestation in the living ovum, in the individual life, and in that line of animals which nearest approach his ancestors, and hence further up to the merely living protoplasm which is neither animal nor vegetable. It then may dawn on us whence are derived the high and lower functions—e.g., speaking and seeing, as well as breathing and walking, and how they have become as they are.
But if we continue to inquire without comparing, we can not arrive at such knowledge; but by merely observing in which way in one instance a function is performing, we may, with great expenditure of labor and ingenuity, time and material sacrifices, find only how it may be or may have been, not how it is and has been. The preference since Galvani's time for the frog as an object of physiological inquiry, the too frequent use of dogs, rabbits, and Guinea-pigs, already called the domestic animals of physiologists; and the levity with which the discoveries made on these few animals, so widely differing from man, have sometimes been applied to the latter, have caused many errors. It is gratifying that at least some of the younger investigators choose also other objects of inquiry, but they should not be the exception. By no means can it be urged that it is too difficult to procure the material, and that in zoölogical gardens physiological laboratories can not
