THE RELATIONS OF PHYSIOLOGY 411 



have stood in the foreground of physiologic interest, which have 

 little or nothing to do with practical medicine. What an immense 

 extent the investigation of the production of electricity in muscles 

 and nerves has reached, in the physiological laboratories and lec- 

 tures, and what could and can practical medicine do with these 

 things? What an exaggeration Ludwig's discovery of the graphic 

 method for the representation of motions has called forth in the 

 physiologic instruction of the physician? We have even heard the 

 opinion expressed that only that which could be demonstrated 

 graphically should be taught in physiology. Yes, many physi- 

 cians believe that they must go to practice with a Marey's sphyg- 

 mograph in their pocket. And of what use have all these sphyg- 

 mograms and respiration curves been in modern practice? They 

 have disappeared. The graphic pocket apparatus lies among the 

 old rubbish. Practical medicine has cast aside the false exactness 

 which was imposed upon it. Instead of these, it has itself created 

 general physiologic conceptions. Our entire knowledge of the 

 physiologic protection of the normal body against infection, our 

 whole experience with regard to artificial and natural immunity, 

 which plays so dominant a role in modern medicine, did not arise 

 from physiologists. The enormous development of this whole 

 branch of medicine shows plainly the need of medicine for physi- 

 ology, and especially for basic and general physiologic concep- 

 tions. 



It appears to me that general physiology may have a very stim- 

 ulating effect upon the further development of our medical opin- 

 ions. There is one branch of medicine with which physiology has 

 the very closest relationship; that is, the teaching of stimuli and 

 their effects. 



It is really a very paradoxical phenomenon, that physiology 

 has worked for centuries with various methods of stimulation in 

 their largest as well as in their smallest relationships, without 

 ever investigating systematically the general laws of the effects of 

 stimuli, without even attempting a sharp and general definition 

 of the meaning of stimulus. Only the more recent development 

 of physiology has brought about a closer approach to this ques- 

 tion, and has already extended the truth to a certain degree, 

 although many important points still wait explanation. The study 

 of the effects of stimuli, in a large number of the most different 

 independent and tissue-forming cells, has here permitted a fairly 

 definite determination of laws, and, above all, has permitted the 

 sharp fixation of the general conception of stimulus. To-day we 

 can define this, in its most general sense, as a change in the ex- 

 ternal influences which affect the existing condition of a living 

 system. Thus, the effects of stimuli find their expression in a quan- 



