CHAPTER III 



THE CHARACTERISTICS OF STIMULI 



Contents: The quality of the stimulus. Positive and negative alterations 

 of the factors which act as vital conditions. Extent of the alteration 

 in vital conditions or intensity of the stimulus. Threshold stimuli, 

 sub-threshold, submaximal, maximal and supermaximal intensities of 

 stimulus. Relations between the intensity of stimulus and the amount 

 of response. The Weber and Fechner law. All or none law. Time 

 relations of the course of the stimulus. Form of individual stimulus. 

 Absolute and relative rapidity in the course of the stimulus. Duration 

 of the stimulus after reaching its highest point. Adaptation to per- 

 sistent stimuli. Series of individual stimuli. Rhythmical stimuli. 

 The Nernst law. 



We have found that stimuli are alterations in the external vital 

 conditions and that the irritability of living substance consists in 

 the capability to respond to stimuli by changes of the vital pro- 

 cesses. It now behooves us in the interest of experimental 

 research to investigate the relations between the nature of the 

 alterations in the external vital conditions on the one hand, and 

 that of the alterations of the vital process on the other ; that is to 

 say, to systematically study the effects of stimulation on the living 

 organism. For this purpose it is above all necessary to become 

 acquainted with the almost countless numbers of alterations 

 which take place in the external vital conditions of an organism, 

 and to create a systematic scheme of stimulation which differen- 

 tiates and presents in comprehensive order those various ele- 

 mentary factors which, among the innumerable varieties of stim- 

 uli, would prove effectual. For this purpose it is necessary to 

 select the various factors which are involved in an alteration of 

 the external vital conditions. 



The first of these factors is the quality of the stimulus. The 

 external vital conditions are, in short, a series of chemical factors, 

 such as foodstuffs, water and oxygen ; the presence of a cer- 



