1894.] The Scope of Modern Physiology. 385 
man to whom it is customary to give the credit for hav- 
ing outlined the path that was to be followed during his life- 
time and for the generation that has elapsed since his death, 
the teacher, either personally or by his writings, of the vet- 
erans, Ludwig, Du Bois Reymond, Briicke and Helmholtz, 
was Johannes Müller. Miiller’s name will at once suggest the 
one important principle that he formulated, that of specific 
herve energies, but his writings and discoveries cover a wide 
field. His extraordinary knowledge, energy, enthusiasm and 
stimulating power were all-important during a period so rich 
with biological achievements. It is perhaps a fair question, 
whether Magendie, with his marvellous activity as an experi- 
mentalist, may not dispute with Müller the honor of having 
given to the physiology of the past fifty years its character- 
istic trend. Certain it is that he fathered the science in 
France (Claude Bernard was his pupil); that his writings 
were read much across the Rhine; and that the labors of the 
Germans have been, like his, the collecting of facts rather 
than the constructing of systems. Within this half-century 
. the establishing of the two great doctrines of physics, the 
mechanical theory of heat and its greater corollary, the con- 
servation of energy, were of indispensable aid to the develop- 
ment of physiology. The idea of vital force had taken on 
many forms and the controlling principle of life had played 
its part under many titles. But, when it was shown that in 
the inorganic world the various kinds of energy are mutually 
interchangeable, physiologists, long hampered by and impa- 
tient under the old ideas, eagerly siezed upon the new, in fact, 
aided not a little in their discovery, and proved that they 
applied to living things as well as to the not-living—and, with 
this, freedom from unscientific speculation was won ; the ani- 
mal is a machine in a sense more complete than the Cartesian 
one. On the purely physiological side of biology, this is 
undoubtedly the greatest achievement of the present century. 
Until the substance of the plant and the animal body could 
be regarded as subject to the same laws that controlled all 
other matter, much must have remained mysterious and inex- 
Plicable and physiology could not be reckoned as all in alla 
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