EXCITATORY CHARACTER OF SUCTIONAL RESPONSE 377 



increasing the suction of a specimen of Croton in a favourable 

 condition of excitability. We have here a very great en- 

 hancement of the ascensional movement caused by this solu- 

 tion, which would, acting osmotically, have retarded the 

 normal rate. The physiologically excitatory action of strong 

 sodium chloride, however, is not permanent, and the enhanced 

 excitability is followed by depression. The effect on suctional 

 response in such cases, then, is modified by the factor of time, 

 the first enhancement being 

 followed by a fall below the 

 original normal rate of suction. 



The experiments which I 

 have here described show how 

 intimately suctional response is 

 connected with excitatory re- 

 action. Having thus seen that 

 any physiological modification 

 of the tissue is attended by an 

 appropriate change in the rate 

 of suction, it only remains to 

 demonstrate finally the fact that 

 stimulation is attended by a 

 responsive movement of water 

 in a tissue. In order to do this, 

 we should have at our disposal 

 some means of applying 

 stimulus which is capable of 



measurement, capable of graduation, and not in itself of 

 a nature to disturb the delicate balance of the shoshun- 

 graphic record. The end sought after was first to record 

 .the normal rate of suction, and then to observe the 

 effect immediately induced in this by the application of the 

 stimulus, the process of record being uninterrupted mean- 

 while. The only form of stimulus which would comply 

 with these conditions is the electrical, given by tetanising 

 induction shocks, of longer or shorter duration. The possible 

 objections to the use of this form of stimulus are as follows : 



FIG. 222. Effect of Strong NaCl 

 Solution 



The first record shows the normal 

 and the second the exalted rate 

 of suction caused by the reagent. 



