METHODS OF PHYSIOLOGICAL RESEARCH 23 



if he were endowed with the latter's superhuman power of 

 labour. 



Morphology had become independent long before Mtiller. Soon 

 after his death the course of physiology became divided and 

 directed along purely chemical and purely physical paths. 



Movement in the chemical direction was guided by Wohler 

 (1800-1882) and Liebig (1803-1873). In the year 1828 Wohler 

 gave the theory of vital force its death-wound by his epoch-making 

 synthesis,out of purely inorganic substances,of urea, a body produced 

 in nature only by organisms. It had been believed that substances 

 that were produced by the organism were produced only through 

 the activity of vital force ; but here for the first time a very charac- 

 teristic material product of the animal body was manufactured 

 artificially in the chemical laboratory. This synthesis was soon 

 followed by others. Justus von Liebig established new views regard- 

 ing the metabolism of organisms ; and later Voit, Pfltiger, Zuntz, 

 and others, advanced the theory of metabolism further, though not 

 in entire agreement with one another. Physiological chemistry 

 became more and more independent, partly under the influence of 

 Mulder and Lehmann, who first made a survey of the field, and 

 especially under that of Kuhiie, who by his original methods and 

 investigations, particularly upon the chemico-physiological relations 

 of the proteids, diffused new light and expressed his conception 

 of the science in his text-book. Finally, most recently, through 

 the labours of Hoppe-Seyler, Hammersten, Bunge, Halliburton, 

 Baumann, Kossel, and others, physiological chemistry as an inde- 

 pendent science has quite cut itself loose from physiology, to the 

 detriment of the latter. 



E. H. Weber (1795-1878), Volkmann (1801-1877), Ludwig 

 (1816-1895), Helmholtz (1821-1894), du Bois-Reymond (1818- 

 1896), Marey, and others, led the movement in the physical direc- 

 tion. Ludwig mechanically transmitted the rhythmic changes of 

 pressure of the pulse to a moving writing-lever, and made them 

 record themselves upon the smooth surface of paper moved at a 

 uniform rate (Fig. 1). He thus surpassed all others in creating a 

 method of the greatest value in the investigation of the purely 

 physical activities of the animal body. This graphic method proved 

 so extremely fruitful that it found wide employment in physiology. 

 It was used for the graphic representation of muscle-contraction, 

 of respiratory movements, of the heart-beat, etc. In France, Marey 

 developed it to unexpected completeness ; so that now it serves as 

 the most important method of investigation in all researches that 

 deal with the phenomena of macroscopic movement. One other 

 method became fundamentally important in physical physiology, 

 namely, that of the comprehensive and ingenious technique of 

 galvanic stimulation, which was created by E. du Bois-Reymond's 

 classic researches upon the general physics of muscle and nerve. 



