RESPONSE OF EPITHELIUM AND GLANDS 325 



a second reversal of normal response into a"->b' r , under 

 excessively strong stimulation. We are thus enabled to see 

 the theoretical possibility of the reversal of normal response 

 under the two conditions of sub-minimal and super-maximal 

 stimulation. All these phases may not be displayed in the 

 same specimen ; but it may be possible to find different 

 specimens exhibiting one or the other. 



In some cases the difference a b is too small to allow 

 of an appreciable galvanometric effect, and in their higher 

 parts the curves do not cross. In such specimens, then, 

 there is no response under sub-minimal stimulus, and only 

 normal response under increasing intensities, however strong. 

 The only exception to this will take place when fatigue 

 supervenes, a case which will be dealt with presently. I find 

 that this type of response is the most common. 



We have next to consider those cases in which in the 

 sub-minimal region, the difference a b is appreciable, the 

 reversal to normal b'-*a' taking place under higher in- 

 tensities of stimulus. There need not in such an instance, 

 be any second reversal. Here, then, the normal response 

 under moderate or strong stimulus is reversed when the 

 stimulus is sub minimal. An example of this will be given 

 presently. 



Lastly, there may be a type of response in which in the 

 sub-minimal region the difference a b is slight, and the 

 normal b'-+a' is reversed to a"-*b" in the region of excessive 

 stimulation. I shall be able to give an example of this also. 



I have been able, by taking different specimens, to 

 demonstrate the occurrence of these theoretical reversals of 

 response, under sub-minimal and super-maximal stimulation. 

 I have not yet been able to find a single specimen ex- 

 hibiting both reversals, but it is not impossible that this 

 exists. 



The type in which response remains normal throughout 

 a wide range of stimulus-intensity is too -numerous to 

 require special illustration. But this normal response may 

 be reversed under fatigue. Generally speaking, a highly 



