288 Journal of Comparative Neurology and Psychology. 



have to inquire, for instance, what effects sounds which stimulate the auditory 

 organs and cause the animal to become alert, watchful, yet make it remain 

 rigidly motionless, have on the primary organic rhythms of the organism, such 

 as the heart-beat, respiration, and peristalsis. It is also directly in the line of 

 our investigation to inquire how they affect reflex movements, or the reaction 

 time for any other stimulus — what happens to the reaction time for an electrical 

 stimulus, for example, if a loud noise precede or accompany the electrical 

 stimulus. 



III. The Influence of Sounds on Reactions to Other 



Stimuli. 



/. Influence of sound on respiration and visual reactions. — 

 Observations described in my earlier paper prove that respira- 

 tion is modified by sounds, and it was also noted that the 

 attempts of a frog to seize a moving object are reinforced by 

 the sound of a tuning fork.^ 



2. Influence of sounds on tactual reactions. — A more detail- 

 ed study has been made of the influence of sounds on tactual 

 reactions and of the significance of the temporal relations of the 

 stimuli. 



A reflex movement of the leg was chosen as an indication 

 of the action of the stimuli and the influence of sounds was 

 observed under the following conditions. A frog was placed 

 on a saddle-like holder and kept in position by linen bands over 

 the back and a wire screen cap over the head, as shown in Fig. 

 4. Under these conditions the hind legs usually hang free and 

 limp and any movement which may be made by them in 

 response to a stimulus can be read in millimeters from a scale, 

 attached to the holder. This method of measuring the value 

 of stimuli in terms of leg reflex has been used by several other 

 investigators, most recently by Merzbacher. In this connec- 

 tion it is of interest to note that neither Merzbacher nor Ewald 

 were able to detect movements of the leg of the frog in response 

 to sounds. Even the croaking of another frog near by had no 

 apparent effect.^ 



'1. c. p. 634. » 



'Merzbacher, L. Ueber die Beziehungender Sinnesorganezur den Reflex- 

 bewegungen des Frosches. Pfiilger's Arch., 81, 254, 1900. 



