BIOLOGY IN RELATION TO OTHER NATURAL SCIENCES. 441 



daiiieutal idea which finds one form of expression in tlie world of living- 

 beings regarded as a whole — the prevalence of the best — manifests 

 itself with equal distinctness, and plays an equally essential part in the 

 internal relations of the organism in the great science which treats of 

 them — physiology. 



ORIGIN AN]) SCOPE OF MODERN PHYSIOLOGY. 



Just as there was no true philosophy of living nature 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, notwithstand- 

 ing their extraordinary 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 

 successors, was the beginner of a new era. 



Miiller taught in Berlin frota 1833 to 1857. During that time a grad- 

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

 fundamental problem of life. Miiller himself, in common with Trevira- 

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

 regarded what was then called the vis viialis — the Lehenslcraft — as 

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

 a necessary consequence held that phenomena should be classified or 

 distinguished, according to the forces which i)roduced 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 

 knowledge which existed, no obvious physical exi)lanation could be 

 found, were sufficiently explained when they were stated to be depen- 

 dent on so called vital laws. But during the period of Midler's great- 

 est 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 intluencein the same direc- 

 tion on the men of the next generation, teaching them that it was bet- 

 ter and more useful to observe than to philosophize; so that, although 

 he himself is truly regarded as the last of tlte 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 abandonment of theory for fact, 

 of speculation for experiment. Physiologists ceased to theorize because 

 they found something better to do. May 1 try to give you a sketch of 

 this era of progress? 



Great discoveries as to the structure of plants and animals had been 

 made in the course of the i^revious decade, those especially which had 

 resulted from the introduction of the microscope as an instrument of 

 research. By its aid Schwann had been able to show that all organ- 



