822 THE POPULAR SCIENCE MONTHLY. 



sibly be entirely based on mechanics, nor can we meet the difficulty 

 by substituting for " mechanics " the highest physics and chemistry, 

 including consummate molecular mechanics. For physics treats only 

 of phenomena dependent on motion — that is, changes in space, the 

 forces, the causes of motion, and the causes of changes in motion, as 

 formulated by human intelligence, are its proper domain. Chemistry, 

 which ascribes to Nature one single force — that of affinity — because 

 it does not need any other, deals with substances alone, with the vari- 

 ous elements of matter. Processes which can not be attributed to 

 either changes of forces, i. e., change of one force into another, or to 

 changes of substances, i. e., the transformation of the latter through 

 separation and combination, are not physical and not chemical ; con- 

 sequently, neither physics nor chemistry is engaged in their investi- 

 gation. Such processes, however, take place in animate bodies — the 

 feeling of hunger, for instance, which the most thorough physical and 

 chemical inquiry fails to explain, though its necessary conditions and 

 consequences may be ascertained. 



During the fertilization and division of the ovum, during the dif- 

 ferentiation of embryonic forms, during the gradual transformation 

 of fetal and aimless into functionary movements of muscles and nerves, 

 and during the perfection of the organs of sense and of the nerve-cen- 

 ters after birth, a series of processes occur which are entirely outside 

 the domain of both the physicist and the chemist. They are not called 

 upon to deal with the problems of heredity and psychogenesis, as they 

 do not present themselves in the physical and chemical world. 



For the very reason that there is one world only, all dualistic sys- 

 tems are untenable. The mechanical theory asserts, though illogically, 

 that, by means of its one-sided principles, all things will in time be 

 understood. The dualistic or vitalistic theory starts by assuming the 

 existence of a contrast in the world, the forces in the living body being 

 different from those in the crystal, those in the brain not the same as 

 those in the material of which the brain is composed, those in young 

 protoplasm not the same as in the old. Now it devolves upon physi- 

 ology to show how to eliminate this " vitalism " which encumbers its 

 path. Physiological inquiry must attach more importance to the con- 

 ception of evolution. Morphology, in applying the method of evolu- 

 tion in all its departments, has gained a higher repute than ever. The 

 anatomical pbylogenetic history of man, in connection with his em- 

 bryological and later history of development, may indeed furnish an 

 explanation of the marvelous fitness and natural evolution of the hu- 

 man body. 



It is, therefore, surprising that in that domain of the science treat- 

 ing of living bodies, in physiology, or the science of the functions, it 

 hitherto has not been applied at all, or only occasionally and reluct- 

 antly. The neglect is due partly to the erroneous opinion that not the 

 physiological function, but only its substratum the bodily organ, is 



