POSITIVE AND NEGATIVE TURGIDITY-VARIATIONS 63 



animal. From the experiment just described, however, it will 

 be seen that the effect observed by him was in reality due, 

 not to true excitation, but to the hydrostatic disturbance, or 

 indirect effect of stimulus. 



In the next record (fig. 47, c) we see the effect of stimulus 

 applied nearer : that is to say, at a distance of 2 cm. from the 

 proximal contact. Owing to the propinquity of the point of 

 stimulation, the two disturbances are not now sufficiently 

 separated, and the excitatory negative reaction completely 

 masks the hydrostatic positive effect. 



It is thus seen that, as has been said, one method of 

 exhibiting these two effects separately is to apply stimulus 

 at a point so distant from the proximal contact that there 

 is an interval between the arrival of the two waves of hydro- 

 static and excitatory disturbance respectively. It is obvious, 

 then, that if the tissue under experiment be a good con- 

 ductor of excitation, we must place the point of stimulation 

 at a long distance from the first electrode, in order that 

 the effect of excitation may lag sufficiently behind the 

 hydrostatic wave. Similarly, in a bad conductor of excita- 

 tion, it will be the indirect effect alone which will reach 

 the proximal contact, unless the stimulus applied be very 

 near, and very strong. 



In order to distinguish these two opposite effects from 

 each other, I shall in future refer to that hydrostatic 

 effect which causes expansion and galvanometric positivity 

 as ' the hydro-positive effect/ by way of differentiating it 

 from 'the true excitatory effect,' of negative turgidity- 

 variation and galvanometric negativity. 



It has already been said that tissues which exhibit 

 a high degree of conduction are characterised by more 

 or less of protoplasmic continuity. Hence, fibre-vascular 

 elements are relatively good, and parenchymatous tissues 

 bad, conductors of excitation. The cells of the potato tuber 

 for this reason exhibit very little power of transmitting 

 excitation. When, therefore, in experimenting with this 



