ADDRESS. 9 



plants and animals to each other, and to the past and present conditions 

 of their existence — is by far the most attractive. In it those qualities of 

 mind which especially distinguish the naturalist find their liighest 

 exercise, and it represents more than any other branch of the subject 

 what Treviranus termed the ' philosophy of living nature.' Notwith- 

 standing the very general interest which several of its problems excite at 

 the present moment I do not propose to discuss any of them, but rather 

 to limit myself to the humbler task of showing that the fundamental idea 

 which finds one form of expression in the world of living beings regarded 

 as a whole — the prevalence of the best — manifests itself with equal dis- 

 tinctness, and plays an equally essential part in the internal relations of 

 the organism and in the great science which treats of them — Physiology. 



Origin and Scope of Modern Physiglogt. 



Just as there was no true philosophy of living natare until Darwin, 

 we may with almost equal truth say that physiology did not exist as a 

 science before Johannes Miiller. For although the sum of his numerous 

 achievements in comparative anatomy and physiology, notwithstanding 

 their extraordiuaiy number and importance, could not be compared for 

 merit and fruitfulness with the one discovery which furnished the key to 

 so many riddles, he, no less than Darwin, by his influence on his suc- 

 cessors was the beginner of a new era. 



Miiller taught in Berlin from 1833 to 1857. During that time a 

 gradual change was in progress in the way in which biologists regarded 

 the fundamental problem of life. Miiller himself, in common with 

 Treviranus and all the biological teachers of his time, was a vitalist, i.e., 

 he regarded what was then called the vis vitalis — the Lebenshraft — as 

 something capable of being correlated with the physical forces ; and as a 

 necessary consequence held that phenomena should be classified or dis- 

 tinguished, according to the forces which produced them, as vital or 

 physical, and that all those processes — that is groups or series of phe- 

 nomena in living organisms — for which, in the then very imperfect know- 

 ledge which existed, no obvious physical explanation could be found, 

 were sufficiently explained when they were stated to be dependent on so- 

 called vital laws. But during the period of Miiller's greatest activity 

 times were changing, and he was changing with them. During his long 

 career as professor at Berlin he became more and more objective in his 

 tendencies, and exercised an influence in the same direction on the men 

 of the next generation, teaching them that it was better and more useful 

 to observe than to philosophise ; so that, although he himself is truly 

 regarded as the last of the vitalists — for he was a vitalist to the last — his 

 successors were adherents of what has been very inadequately designated 

 the mechanistic view of the phenomena of life. The change thus brought 

 about just before the middle of this century was a revolution. It was not 

 a substitution of one point of view for another, but simply a frank aban- 



