CHEMICAL REAGENTS ON LONGITUDINAL RESPONSE 1 37 



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or contraction as the direct effects of chemical agents, which 

 it would be out of place to treat in detail here. It need only 

 be stated that these effects, which can be very accurately and 

 continuously recorded by the arrangement ot the Optic 

 Lever, are very suggestive. They are found to be modified 

 by the tonic condition of the tissue, the strength of the agent, 

 and the duration of application. Thus, an effect of relaxation 

 may, after a time, pass into the opposite, of contraction. And 

 since these relaxations or contractions of the tissue have a 

 modifying influence on the 

 response, much light on the 

 obscure subject of the effect 

 of drugs becomes possible 

 through this study. I have 

 been able already to obtain 

 several curious and interest- 

 ing results, of which I may 

 here refer to one, in which 

 two drugs, either of which 

 when applied singly would 

 abolish response, and produce death, are made, when 

 applied in succession, to act as antidotes to each other. It 

 is my intention to show in the course of this book that all 

 the physiological phenomena of the animal have the closest 

 correspondence with similar phenomena in the plant, and 

 this being so, an investigation carried out on the lines 

 indicated, with plants, is likely to be of very great import- 

 ance, practically as well as theoretically. 



Fig. 74. Action of Chlorine 



Photographic record, showing normal 

 effect to the left, depressed and 

 almost abolished after introduction 

 of the gas. 



Summary 



The responsive contractions of an organ afford a reliable 

 indication of the excitability of the tissue. 



The physiological changes induced in plant-tissues by the 

 action of chemical reagents are outwardly manifested by 

 modification of response. 



Certain agents, producing great relaxation, reduce the 



