CHAPTER XI 



VARIATIONS OF EXCITABILITY UNDER CHEMICAL 

 REAGENTS 



Induced variation of excitability studied by two methods : (i) direct (2) trans- 

 mitted stimulation Effect of chloroform Effect of chloral Effect of formalin 

 Advantage of the Method of Block over that of negative variation Effect 

 of KHO Response unaffected by variation of resistance Stimulating action 

 of solution of sugar Of sodium carbonate Effect of doses Effect of hydro- 

 chloric acid Di-phasic response on application of potash Conversion of normal 

 negative into abnormal positive response by abolition of true excitability. 



IT has been said in a previous chapter that the electrical 

 response is a true physiological response. This is demon- 

 strated by the fact that, while a vigorous specimen gives 

 strong electrical response of galvanometric negativity, the 

 same specimen, when killed, whether by heat or by poison, 

 ceases to respond. This particular electrical response is 

 thus seen to be a concomitant of physiological efficiency. 

 It follows that, whatever diminishes physiological activity 

 Vf\\\, part passu, modify the amplitude of the response. But 

 in cases in which the death of the tissue is brought about by 

 steam or by poison, it is the last stage only, namely the 

 abolition of response, that can be observed. It is also impor- 

 tant, however, to be able to trace the growth of physiological 

 changes through the concomitant modification of response. 

 In this way it is possible not only to study the gradual onset 

 of death, as induced by a poison, but also the action of other 

 chemical agents, some of which might be of such a nature 

 as to induce exaltation, others depression, and still others^ 

 like the narcotics, a temporary abolition of the electrical 

 response, 



K 



