CHAPTER X 



THEORIES CONCERNING DIFFERENT TYPES OF RESPONSE 



The chemical theory of response — Insufficiency of the theory of assimilation and 

 dissimilation to explain fatigue and staircase effects — Similar responsive effects 

 seen in inorganic substances — Molecular theory — When molecular recovery is 

 complete, responses uniform : when incomplete, fatigue brought about by 

 residual strain — Fatigue under continuous stimulation, in inorganic substance, 

 in plant, and in muscle — Staircase effect brought about by increased molecular 

 mobility : examples seen in inorganic substance, and in living tissues — No sharp 

 line of demarcation in the borderland between physical and chemical phenomena 

 — Molecular changes attended by changes of chemical activity — Unequal 

 molecular strain gives rise to a secondary series of chemical actions— Volta- 

 chemical effect and by-products — Supposition that response always dispropor- 

 tionately larger than stimulus, not justified — Existence of three types : (i) 

 response proportionate to stimulus ; (2) response disproportionately greater than 

 stimulus ; (3) response disproportionately less than stimulus — Instances of 

 stimulus partially held latent : staircase and additive effects ; multiple response ; 

 renewed growth. 



It has already been shown, in previous chapters, that the 

 various types of response met with in animal tissues are 

 exactly paralleled, even in detail, in the response of plants ; 

 and numerous further instances of this fact will be met with 

 in the course of the present work. It would thus appear 

 that the theoretical explanation of either class of responses 

 must be applicable to the other also. Existing theories 

 regarding animal response, however, have not yet been found 

 sufficient to meet all the difficulties of the case, and it is 

 probable that the larger data now made available by the 

 inclusion of response in plants, may go far to throw light 

 on certain obscurities which are at present regarded as 

 perplexing. 



Chemical theory of assimilation and dissimilation. — 

 The theory which is generally accepted at present may be 

 referred to briefly as chemical. According to it, living matter 



