1894.] The Scope of Modern Physiology. 473 
THE SCOPE OF MODERN PHYSIOLOGY. 
By FREDERIC S. Ler. 
(Continued from page 388.) 
Three achievements of the present period have shown inves- 
tigators how broad their science really is. First, the establish- 
ing of protoplasm as the physical basis of life, and of its sub- 
stantial identity in plants and animals by Dujardin, Von Mohl, 
and Max Schultze, showed that the really fundamental prob- 
lems of life and action had heretofore not been grasped; that 
the essential laws of protoplasmic activity apply to the whole 
organic world ; and hence that any physiology which confines 
itself rigidly to either plants or animals to the exclusion of the 
other is a one-sided science. Second, the cell-theory of Schlei- 
den and Schwann demonstrated that sooner or later many 
functions must be traced back to the cell, and that a cellular 
physiology is the key to a large proportion of the problems aris- 
ing in the biological world. Third, the work of Darwin, based, 
as it was, upon physiological principles, showed that the action 
of the environment upon the individual and upon the species, 
as well as the action of the organism upon the environment, 
was an almost unworked field of the richest promise; that 
all physiology, in order to be complete, must be comparative ; 
that there is an ontogenetic and a phylogenetic evolution of 
function ; and that the physiological laws of heredity were yet 
to be discovered. 
` Let us examine these ideas briefly. The necessity of under- 
` Standing the physiology of undifferentiated protoplasm is ob- 
vious, for there we find function in its simplest and most 
generic form. The phenomena of projection and retraction of 
Pseudopodia in the Amoeba are doubtless the key to the com- 
Plex processes of contraction and relaxation of striped muscu- 
lar tissue. It is not at all improbable that the action of light 
=~ upon the retina is a specialized derivative of the heliotropic 
Phenomena of the simplest plants and animals. Four years 
