192 BiULUGV AND ITS MAKERS 



presence, with a nc^ble head, ihe eyes full at once of thought 

 and kin(hiess, he drew llie look of observers upon him wher- 

 ever lie api)eare(L As he walked in llie streets passers-by 

 mij^ht be heard to say' I wonder who that is; he must be 

 some dislin,u;uished man.' " 



Two Directions of Growth. — Physiology, established on 

 the broad foundations of M tiller, developed along two inde- 

 })endent pathways, the physical and the chemical. We find 

 a group of physiologists, among whom Weber, Ludwig, 

 Du Hois-Revmond, and Helmholtz were noteworthy leaders, 

 devoted to the investigations of physiological facts through 

 the application of measuremicnts and records made by ma- 

 chinery. \\ iih these men came into use the time-markers, the 

 myographs, and the ingenious methods of recording blood- 

 pressure, changes in respiration, the responses of muscle and 

 nerve to \arious forms of stimulation, the rate of transmiission 

 of nerve-currents, etc. 



The investigation of vital activities by means of measure- 

 ments and instrumental records has come to represent one 

 especial phase of modern physiology. As might have been 

 j^redicted, the discoveries and extensions of knowledge re- 

 sulting from this kind of experimentation have been remark- 

 able, since it is obvious that permanent records made by 

 mechanical devices will rule out many errors; and, moreover, 

 they afford an ojjportunity to study at leisure phenomena 

 that occu])y a very brief time. 



Tlie other marked line of physiological investigation has 

 been in the domain of chemistr}% where W^ohler, Liebig, 

 Kiihne, and others have, through the study of the chemical 

 changes occurring in its body, observed the various activities 

 that take place within the organism. They have reduced all 

 tissues and all parts of the body to chemical analysis, studied 

 the chemical changes in digestion, in respiration, etc. The 

 more recent observers have also made a particular feature of 



