332 COMPARATIVE ELECTRO-PHYSIOLOGY 



excitatory reaction may exhibit itself in different parts, even 

 of the same organ, by mechanical movement and secretion 

 respectively, according to the facilities which one or the other 

 portion offers. 



That the phenomenon of contraction is behind the ex- 

 citatory expulsion of water in a vegetable organ, would 

 appear highly probable from certain results obtained in the 

 electrical response. The stimulation of an ordinary vegetable 

 tissue gives rise to two distinct electrical effects at a distance. 

 The first of these is the arrival of the hydro-positive effect of 

 galvanometric positivity, with positive turgidity-variation. 

 The second is the wave of true excitation, with its character- 

 istic of negative turgidity-variation and concomitant gal- 

 vanometric negativity. The first, consisting, as this does, 

 of a hydrostatic blow delivered at a distance, can only, it 

 appears to me, be ascribed to an active process of contrac- 

 tion, causing the squeezing- out of water in the excited region. 

 A passive escape of fluid, due to mere permeability-variation, 

 could not, as I think, originate that impulsive hydrostatic 

 shock which is transmitted to a distance. For such a result 

 to take place an active expulsion would seem to be 

 requisite. 



In view of these facts, is it necessary to hold the doctrine 

 of discontinuity, or, when there is evidence in its favour, are 

 we to believe in the continuity of these apparently different 

 reactions ? The excitatory reactions of different classes of 

 tissues have hitherto been regarded as different, chiefly 

 because some were looked upon as motile, and others as 

 non-motile ; muscle, for example, was held to be typical of 

 the first, and nerve of the second, of these classes. In this 

 case of the nerve, it has been believed that there was no 

 visible manifestation of the excitatory change. I shall, 

 however, be able to show that even this supposition is 

 incorrect, since the excitatory reaction in the nerve is in fact 

 attended by contraction. The electrical indication of gal- 

 vanometric negativity which is concomitant with contraction 

 in contractile tissues, is also obtained in the case of excited 



