386 The American Naturalist. ; [May, 
natural science. Psychology has always been hampered by 
the speculations of the system-loving metaphysicians. More 
actual fact and less conjecture are essential to the scientific 
method; and the scientific method is the method of progress. 
Following this freedom from the doctrine of vital force, physi- 
ology has developed actively along two main lines, the chemi- 
cal and the physical including the mechanical, and is now 
often defined as the chemistry and the physics of living mat- 
ter. An astonishing number of discoveries have been made, 
and the outlines that were sketched by Galen and Harvey and 
Haller and Müller and Magendie have been filled in with 
remarkable rapidity and completeness. 
_ Let us consider for a moment the prominent characteristics 
of the work of this period. In the first place, Vertebrates 
have received more attention and have been the subject of 
more systematic investigation than Invertebrates. And 
among the Vertebrates, with the exception of the indispensable 
frog, which, however, is rarely regarded as a finality in : 
the Mammals, being nearest to man have been most studied. 
Second, the number of forms used is very small; it is prob- 
ably safe to say that the genera employed in four-fifths of the 
researches could be counted easily upon the fingers of the two 
hands. Third, adult animals have been used almost exclu- 
sively. Fourth, the study of organs has prevailed, i. e the 
investigator has endeavored to discover the chemical, physical 
and mechanical laws by which the heart, the lungs, the 
glands, the muscles and the brain perform their respective 
tasks. These characteristics are the natural outcome of the 
birth and growth of the science. They indicate that, although 
the results accomplished are widespread and of the great 
value, there are left almost untouched still wider fields. The 
achievement of so much, however, along the lines of the i 
is stimulating to the student of to-day, for it has made pom 
ble the more rapid development of the science in the A 
directions, in which it is now tending. To these we sha 
return shortly. 
. : . ‘ail 
I think that the historian of the present period will not fa! 
to be struck by the comparative paucity of hypothesis 
“ 
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