PREFACE 



The lectures on irritability here published were held at the 

 University of Yale in October, 1911. When the authorities of 

 that University honored me by an invitation to give a course of 

 Silliman memorial lectures, I accepted with the more pleasure as 

 it furnished me with the opportunity of summarizing the results of 

 numerous experimental researches carried out with the assist- 

 ance of my co-workers during the course of more than two 

 decades in the physiological laboratories of Jena, Gottingen and 

 Bonn, to unite therewith the results obtained by other investi- 

 gators and thus present a uniform exposition of the general effects 

 and laws of stimulation in the living substance. I have long 

 entertained this plan and this for the following reason : 



The physiologist, the zoologist, the botanist, the psychologist, 

 the pathologist, have to deal, day in, day out, with the effects of 

 stimulation on the living substance. No living substance exists 

 without stimulation. In the vital manifestations of all organisms 

 the interplay of the most varied stimuli produces an enormous 

 and manifold variety of effects. Experimental biological science 

 employs artificial stimulation as the most important aid in the 

 methodic production of certain effects of stimulation. The num- 

 ber of researches in which special effects of stimulation are 

 treated is endless. Nevertheless the systematic investigation of 

 the effects of stimulation have, curiously enough, been strangely 

 neglected. Although countless results of individual effects of 

 stimulation have been studied, the attempt has never been made 

 to establish a general physiology of the laws of stimulation and 

 consider it as an independent problem. This circumstance induced 

 me to systematically investigate the general laws of the effect of 

 stimulation. In the fifth and sixth chapters of my book on 

 general physiology the results of these studies are recorded for 

 the first time. Since then, especially during our own researches 

 on the general physiology of the nervous system, a great number 



