VARIOUS TYPES OF RESPONSE 8/ 



vegetable tissues, again, where there is no active circulation 

 of renovating material, the same effect, and its removal after 

 a period of rest, are observed. Thus the difficulties en- 

 countered in explaining fatigue, on purely chemical con- 

 siderations, are great enough ; but still greater are those 

 difficulties which arise when we come to deal with the stair- 

 case effect typically shown in cardiac muscle in which 

 successive responses to uniform stimuli exhibit a gradual 

 enhancement of amplitude. The results obtained here are 

 in direct opposition to the theory described ; for in this 

 particular case we have to assume that the same stimulus 

 which is usually supposed to cause a chemical breakdown, 

 has become efficient to induce an effect exactly the reverse. 



Of the two antagonistic elements in the electrical response, 

 moreover, it is the positive which is supposed to be associated 

 with the assimilative, and the negative with the dissimilative 

 change. If this supposition were correct, however, it would 

 be natural to expect that the positive response would be 

 manifested predominantly in vigorously growing tissues, in 

 which assimilation must be at its greatest Fatigued tissues 

 on the other hand, in which dissimilatory changes are sup- 

 posed to be predominant, should manifest negativity as their 

 characteristic response ; moribund tissues, in contrast with the 

 actively growing, might also be expected to exhibit respon- 

 sive negativity. In actual fact, however, the very reverse is 

 the case. For in vigorous tissues, normal response is by 

 galvanometric negativity ; and it is the over-fatigued or 

 moribund which characteristically exhibit the positive re- 

 sponse. 



It would be difficult again to conceive of assimilation 

 and dissimilation in the case of inorganic matter. Yet even 

 in inorganic matter we find reproduced all the various types 

 met with in the response of living tissues : namely, uniform 

 response, the staircase effect, and fatigue. Response being 

 really due to molecular upset from a condition of equilibrium, 

 we can see how different forms of responsive expression will 

 occur, according to the various molecular conditions of the 



