MULTIPLE AND AUTOMATIC RESPONSE 281 



a second. This seems very high compared with the latent 

 period of Mimosa, which is ■ 1 second. Perhaps this difference 

 may be due to certain characteristics that mark the response 

 of Biophytum. In animal tissues it is found that while 

 the singly responding skeletal tissue of the frog has a latent 

 period of about *oi second, its multiple responding cardiac 

 tissue has a latent period of about *i second, or ten times as 

 long. We shall presently see that the leaflet of Biophytum 

 exhibits multiple response. 



If a second stimulus be applied a short time after the first, 

 it is found that it is ineffective unless a certain minimum 



Fig. 132. — Record giving the latent period of the leaflet of Biophytum. 

 Frequency of vibration of recorder 10 times per second. 



interval of time elapses between the two. In these circum- 

 stances the leaflet takes no account of the second stimulus, 

 becoming apparently refractory to it. The minimum 

 interval that must elapse before the second stimulus can 

 be effective — the refractory period — varies somewhat in 

 different specimens. In Biophytum it is usually 10 seconds. 



Response on All-or-none Principle 



In a previous chapter I have given the record of a 

 response in Biophytum under a single stimulus (fig. 15). 

 We will now study the effect of increasing intensities of 

 stimulus on the amplitude of response. We have seen 

 that in the case of Mimosa increasing intensities of stimulus 

 induce, generally speaking, increasing amplitudes of response, 



