372 Dr. Philip on Stimulants and Sedatives. [Nov- 



Article VII. 



On Stimulants and Sedatives. By Dr. Wilson Philip. 



(To Dr. Thomson.) 



DEAR SIR, Worcester, Sept. 28, 1818. 



In compliance with your request, I trouble you with a few 

 Observations in illustration of the following remarks in the 254th 

 page of the second edition of my Inquiry into the Laws of the 

 Vital Functions ; namely, " A moderate application of every 

 agent appears to act as a stimulus ; and excessive application of 

 it as a sedative. The quantities which act as stimulus and 

 sedative bear no particular proportion to each other, but in differ- 

 ent agents exist in every possible proportion." 



It appears on the most cursory view of the phenomena of life 

 that they depend on a capacity of action in living parts and the 

 operation of agents capable of exciting them. Thus the heart 

 possesses the power of contraction, but it soon becomes inactive 

 if the blood is withdrawn. The degree of excitement produced 

 is proportioned to the force and continuance of the exciting 

 cause and degree of excitability possessed by the part acted on. 

 By the action of the stimulus, the excitability is always impaired, 

 and by its continued action at length exhausted. Thus excite- 

 ment continues, unless the agent is withdrawn, till the part is so 

 far deprived of its excitability that it will no longer obey the 

 same degree of the same agent. To produce further excitement 

 a more powerful agent must be applied, or the excitability of the 

 part acted on must be increased. 



The excitability is, within certain limits, increased by the 

 abstraction of agents. Thus, for example, our sensibility, one 

 species of excitability, is exhausted by the various agents which 

 affect us during the day ; and we find by degrees that the same 

 agents no longer excite us. If more powerful agents are not 

 applied, we soon fall into a state of insensibility, sleep, during 

 which the operation of the usual agents being withdrawn, we 

 again become sensible to these agents. 



Such are the more evident laws of excitability ; and it would 

 be easy, I think, to prove that they are the laws which regulate 

 the cerebral system in a state of health. But it has been main- 

 tained that the same laws regulate the excitability of every part 

 of the animal. To this position a very obvious objection occurs. 



When the eye becomes wearied with seeing, the ear with 

 hearing, &c. they cease to be excited ; their excitability is thus 

 allowed to accumulate, and they are again fitted for their func- 

 tions : they are not concerned in the preservation of life. An 

 animal may be in perfect vigour, as far as relates to the powers 

 on which his existence depends, although he neither sees nor 

 hears. The vital powers remaining in sleep restore vigour to the 



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