824 THE POPULAR SCIENCE MONTHLY. 



apparatus, an ante-stomach whose history of evolution, covering thou- 

 sands of years, distinctly shows the increasing demands for digestibil- 

 ity 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 sim- 

 ply 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, or- 

 ganic retrogression. 



In applying this principle to the physical and mental activities of the 

 healthy and the sick human being, physiological inquiry must of neces- 

 sity 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 evolv- 

 ing 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 182G, Johannes Miiller. 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 in- 

 stance 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 dis- 

 coveries 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 ma- 

 terial, and that in zoological gardens physiological laboratories can not 



