192 BIOLOGY AND ITS MAKERS 



presence, with a noble head, the eyes full at once of thought 

 and kindness, he drew the look of observers upon him wher- 

 ever he appeared. As he walked in the streets passers-by 

 might be heard to say ' I wonder who that is; he must be 

 some distinguished man.' 



Two Directions of Growth. Physiology, established on 

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

 pendent pathways, the physical and the chemical. We find 

 a group of physiologists, among whom Weber, Ludwig, 

 Du Bois-Reymond, and Helmholtz were noteworthy leaders, 

 devoted to the investigations of physiological facts through 

 the application of measurements and records made by ma- 

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

 rnyographs, and the ingenious methods of recording blood- 

 pressure, changes in respiration, the responses of muscle and 

 nerve to various forms of stimulation, the rate of transmission 

 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 

 predicted, 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 opportunity to study at leisure phenomena 

 that occupy a very brief time. 



The other marked line of physiological investigation has 

 been in the domain of chemistry, where Wohler, Liebig, 

 Ktihne, 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 



