REVIEW OF RESPONSE, SIMPLE AND MULTIPLE 713 



occurs when, under uniform stimuli, responses are alternately 

 large and small. These alternations sometimes show them- 

 selves in groups. Under continuous stimulation, again, this 

 periodic fatigue exhibits itself by response of an oscillatory 

 character. 



(V) Staircase response. — The tissue is sometimes in a 

 relatively sluggish condition, and by the absorption of 

 stimulus the molecular mobility is gradually increased. The 

 effect of this is seen in the amplitude of successive responses, 

 increasing in a staircase manner. 



It is usually supposed that response is brought about by 

 a chemical run-down of energy, of an explosive character. 

 The external stimulus is thus supposed to act as it were 

 on a trigger, to release the latent energy. The response 

 is hence assumed to be disproportionately larger than the 

 stimulus. That this cannot, however, hold good in all 

 cases is clear ; for the tissue is often found to absorb a 

 certain proportion of the incident stimulus, the immediate 

 expression of response being thus disproportionately smaller 

 than stimulus. The energy of the system is now found, 

 instead of being lowered, to be raised above par. The 

 internal energy thus held latent is sometimes seen, as 

 in the case of strongly stimulated Biophytum, to find 

 expression later by multiple response. In the case of 

 growth-response, again, it is a variable fraction of incident 

 stimulus that finds immediate expression in the direct effect 

 of retardation of growth, whereas the absorbed component 

 gives rise to the subsequent responsive effect of an enhanced 

 rate of growth. Referring to the former of these as the 

 direct, and to the latter as the indirect, effect of stimulus, it 

 is found that the sum of the two remains approximately 

 constant. Below the optimum tonic condition it is found 

 that the indirect effect is relatively the larger, but near the 

 optimum this relation is reversed, and the direct effect is 

 the larger. In a sub-tonic condition stimulus produces little 

 or no direct effect, it being utilised to produce the indirect 

 effect of enhanced growth. At the optimum, on the other 



