REVIEW OF RESPONSE OF ANISOTROPIC ORGANS 703 



stimulation which is equal and simultaneous. In order to do 

 this, we may employ such a non-electrical form of stimu- 

 lation as the mechanical or the thermal. For this it is 

 possible to employ (i) the Vibratory Stimulator; (2) the 

 Rotary Mechanical Stimulator ; or (3) stimulation by thermal 

 shocks. When results are obtained according to these 

 methods, there can be no uncertainty as to those compli- 

 cations of effects which might conceivably arise when the 

 electrical form of stimulus is employed. The last-named 

 may, however, be used without misgiving, when stimu- 

 lation is effected by equi-alternating shocks. The ordinary 

 RuhmkorfFs make- and break-shocks are not suitable for 

 this purpose, inasmuch as the effective intensity is unequal 

 for make and break, besides which the polarisation-effect may 

 not be exactly neutralised. The equi-alternating shocks, 

 from which these defects have been eliminated, are obtained 

 by means of (i) a rotary reverser in the primary coil (fig. i/o), 

 or (2) a motor-dynamo (fig. 172). The responses again, 

 under these electrical forms of stimulation, may be photo- 

 graphically recorded as either the direct or the after-effect of 

 stimulus. It was shown, by the employment of all these 

 various methods of stimulus, mechanical, thermal, and elec- 

 trical, that the responsive current to be obtained with an 

 anisotropic organ was definite in direction, being always, 

 under normal conditions, from the more excitable B to the 

 less excitable A. I shall now proceed to recapitulate briefly 

 the results obtained by these methods in various cases of 

 anisotropic tissues, such as skin, epithelium, glands, animal, 

 and vegetal digestive organs, and electric organs generally. 



Taking first the skin of tomato it has been shown that 

 the separate responses of the outer and inner surfaces are 

 unequal. The outer, owing to cellular modification under 

 the stimuli of the environment, gives only a feeble negative 

 response, whereas the internal surface gives a much stronger 

 normal response by galvanometric negativity. On simul- 

 taneous excitation of both inner and outer surfaces, the 

 responsive current is found to flow from the inner to the 



