446 BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 



revolution wliicli tlie Darwinian epocli brouglit about in the views 

 entertained by naturalists of the relations of plants and animals to 

 each other and to their surroundings. 



It has been said that every science of observation begins by going 

 out botanizing, by which, I suppose, is meant that collecting and record- 

 ing observations is the first thing to be done in entering on a new field 

 of inquiry. The remark would scarcely be true of jihysiology, even at 

 the earliest stage of its develoi)ment, for the most elementary of its 

 facts could scarcely be picked up as one gathers flowers in a wood. 

 Each of the processes a\ hich go to make up the complex of life requires 

 separate investigation, and in each case the investigation must consist 

 in first splitting up the process into its constituent phenomena, and 

 then determining their relation to each other, to the process of which 

 they form part, and to the conditions under which they manifest them- 

 selves. It will, I think, be found that even in the simplest inquiry into 

 the nature of vital processes some such order as this is followed. Thus, 

 for example, if muscular contraction be the subject on which we seek 

 information, it is obvious that, in order to measure its duration, the 

 mechanical work it accomplishes, the heat wasted in doing it, the elec- 

 tro-motive forces which it develops, and the clianges of form associated 

 with these phenomena, special modes of observation nnist be used for 

 each of them, that each measurement must be in the first instance 

 separately made, under special conditions, and by methods specially 

 adapted to the required purpose. In the synthetic part of the inquiry 

 the guidance of experiment must again be sought for the purpose of 

 discriminating between apparent and real causes, and of determining 

 the order in which the phenomena occur. Even the simplest exj)eri- 

 mental investigations of vital processes are beset with difticulties. For, 

 in addition to the extreme complexity of the phenomena to be examined 

 and the uncertainties which arise from the relative inconstancy of the 

 conditions of all that goes on in the living organism, there is this addi- 

 tional drawback, that, whereas in the exact sciences experiment is 

 guided by well-ascertained laws, here the only principle of universal 

 application is that of adaptation, and that even this can not, like a 

 law of physics, be taken as a basis for deductions, but only as a sum- 

 mary expression of that relation between external exciting causes and 

 the reactions to which they give rise, which, in accordance with Tre- 

 viranus' definition, is the essential character of vital activity. 



THE SPECIFIC ENERGIES OF THE ORGANISM. 



When, in 1826, J. Miiller was engaged in in^'estigatingthe physiology 

 of vision and hearing, he introduced into the discussion a term, " spe- 

 cific energy," the use of which by Helmholtz* in his physiological writ- 



* " Handb. der physiologischeu Optik," 1886, p. 233. Helmholtz uses the word in 

 Ihe plural, the "energies of the ueives of special sense." 



