CARL LUDWIG. 329 



vention cannot be overrated. We younger workers are so 

 accustomed to the graphic method, and look upon it as such 

 a matter of course, that we can hardlv conceive the extent 

 to which it has revolutionised biological science. The ob- 

 serving eye replaced the speculating mind in studying func- 

 tions of animal life, hitherto inaccessible to any experimental 

 research. The course of the most intricate processes and 

 their dependence on various conditions, natural and artificial, 

 could be expressed as measurements of tracings on a surface 

 that could be kept as an objective document for an indefinite 

 time. It is the want of the graphic method in previous 

 generations that accounts for their prevailing ignorance and 

 for their often absurd ideas about the most common actions 

 of life, albeit in those generations there were plenty of 

 mental achievements of the most brilliant kind. 



Only three years after the invention of the graphic 

 method, Helmholtz made by its use — besides the appliance 

 of the Jouillet method of measurement of time — his great 

 discovery regarding the velocity of nerve-energy, by which 

 the foundation of a new branch of biological science, namely, 

 that of experimental psychology, was laid. 



In close connection with the kymographion, and supple- 

 mentary to it, appeared in Ludwig's laboratory a great number 

 of other new instruments for estimating time-relations ; these 

 were chronographs, clockworks for making and breaking 

 electric currents at given intervals, the rheometer, used to 

 measure the amount of blood Mowing through a vessel in a unit 

 of time, instruments for study of the pulse (sphygmographs), 

 etc. P'or the examination of the gases in the blood and in 

 the lymph, Ludwig constructed a gas-pump besides various 

 other appliances, which served for a simplification of the 

 measurement of them. The Leipsic physiological laboratory 

 with its complete arrangements for graphic and measuring- 

 methods, wherever vital processes, in spite of their subtlety, 

 permitted, has served as model for all institutions since 

 erected. When this year the third International Physio- 

 logical Congress met in the new and magnificent institution 

 of Berne, Professor Hugo Kronecker, himself a pupil of 

 Ludwig, and universally regarded as the heir of his genius 



