THE RELATIONS OF PHYSIOLOGY 413 



come in, and here general physiology must come into the closest 

 relation with medical diagnosis, if further progress and deeper 

 knowledge are desired. 



But therapeutics can, as little, do without an accurate know- 

 ledge of the effects of stimuli. The fundamental peculiarity of 

 living substance, automatic regulation, is of the first importance 

 for therapy, as Ewald Hering first showed clearly. If any stimulus 

 has disturbed the balance of normal metabolism or kinetics, it 

 restores itself immediately after the cessation of the stimulus, 

 unless the latter has exceeded certain limits, in which case death 

 results. The therapeutic test of the physician consists to a great 

 degree in preventing the harmful effects of stimuli, for the organ- 

 ism cures itself. "Medicus curat, natura sanat." Naturally the 

 use of any therapeutic measure requires the same profound know- 

 ledge of the phenomena of stimulation, for every therapeutic in- 

 fluence upon the organism is, essentially, a stimulus. And it is 

 evident that the physician should only use stimuli whose effects he 

 knows accurately, if he will effect a definite result of stimulation, for 

 therapeutic purposes. For this reason pharmacology and toxicology, 

 as well as therapy, base a large part of their usefulness on the phe- 

 nomena and experiences of the physiology of stimulation. If they 

 will proceed in a truly scientific manner, they must answer the 

 same questions, and proceed in the same way, in the demonstra- 

 tion of the effects of medicaments and poisons, as that which was 

 described in connection with diagnosis. Thus, in the whole realm 

 of medicine, we are more and more forced to the necessity of the 

 closest union with general physiology. 



I might conclude here, but I feel that I should touch at least 

 superficially a question which is much discussed to-day, that of 

 the relation between physiology and psychology. 



You will say, if physiology is the study of the phenomena of 

 life, it must include psychic as well as physical phenomena, and 

 psychology is thus nothing more than a branch of physiology. 

 But the question is really not so simple; the psychic phenomena 

 of any other organism are, of course, accessible to our mechanical 

 analysis, but in the analysis of our own psychic phenomena we must 

 put aside the principles and methods of physics and chemistry. Also, 

 it has been shown that the chain of physical occurrences in the 

 organism cannot undergo an interruption of continuity anywhere, not 

 even in the brain. A physical process is always, and only, the result 

 of another physical process, and the starting-point of a third. Thus 

 there remains in the series of physical processes no place for any 

 psychic link. We have, however, demonstrated that psychic pro- 

 cesses only occur when definite physical conditions are fulfilled, 

 so that the question concerning the relation of physiology to psych- 



