CYCLIC MOLECULAR VARIATION 641 



sphere of action. Thus, continuous absorption of sugar 

 could not for a long time bring about sufficient accumulation 

 to cause depression. With copper sulphate, however, the 

 case is different. Here, the constant absorption of the 

 sub-tonic stimulatory dose would cause accumulation in the 

 system, and thus ultimately bring about the death of the 

 plant.' 1 



From all this it is clear that the progress of medicine may 

 be greatly facilitated when the attention of investigators is 

 drawn to the importance of the molecular aspects of the 

 phenomena with which they have to deal. Thus, in examin- 

 ing the action of drugs, a threefold question is seen to arise. 

 It must first be determined what is the nature of the respon- 

 sive molecular change induced by the given reagent under 

 normal conditions. The second matter of inquiry is, What is 

 the critical dose, above and below which opposite effects may 

 be expected ? And, finally, as the nature of the response has 

 been seen to be influenced by the part of the molecular curve, 

 at which the responding tissue has arrived, when the chemical 

 reagent is applied, it lollows that an important element in 

 the problem .lies in the determination of the tonic condition 

 of the tissue. How important is this last factor will be seen 

 from an experiment to be described at the end of the present 

 chapter, where an identical course of treatment in one 

 condition of the tissue revives it from inanition, and in 

 another hastens its death. 



I have shown that when the condition of the substance 

 is transformed from C to E, the response also is reversed 

 from normal negative to abnormal positive. I shall now, 

 therefore, proceed to show that in the course of this 

 transition there is an intermediate stage of diphasic 

 response. Before exhibiting this in the case of nerve, I shall 

 give an interesting record in which the same thing is seen to 

 take place in the mechanical response, of fatigued indiarubber. 

 Before the onset of fatigue, the normarcontractile 'responses 

 were large, but at that stage that is to say before the record 



1 Bose, Plant Response, p. 488. 



T T 



