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WHAT IS A STIMULANT? 
BY FRANCIS E. ANSTIE^ M.D. 
■ 
T he popular idea of tlie mode in wMck stimulants influence 
the animal organism may be briefly summed up. These 
agents are supposed to quicken vital motions — muscular, 
nervous, secretory, circulatory, &c. ; and the degree of quick- 
ening is supposed to indicate the amount of stimulation. 
This notion is so entirely incorrect that physiologists can 
hardly do better service to the public than by helping forward 
a better understanding of this fundamental question in vital 
science. 
If the word stimulus is to be retained in use at the present 
time it must be employed only in a figurative sense. We 
have left behind us the days of a metaphysical physiology 
which assumed the existence of a mortal soul presiding over 
the functions of the body, and possessed of emotions, in 
virtue of which it responded to the impressions of stimuli. 
We are leaving behind us, too, inevitably, though with 
reluctance, the unsatisfactory substitutes for the mortal 
soul which we have created by employing dynamical terms, 
such as vital force ” and the like, which imply, in fact, only 
the appearance and not the reality of a change from the old 
metaphysical method of speculation. It is to be hoped that, 
for the future, we shall cease to employ that combination of 
the petitio iJfmcijni with the argmnentiim in circulo which 
first assumes the existence in the organism of a capacity of 
being stimulated, and then takes the licence of a traveller in 
fabulous regions to describe the reactions of an unknown and 
unknowable vis vitce. 
If stimulus mean anything in the present state of physio- 
logical science, it must certainly signify that kind of agent 
which restores natural functions to their natural level and mode 
of action. Consequently it will be applicable with far greater 
frequency to an action which delays rather than to one which 
accelerates the speed of vital motions. No fact is more 
conclusively demonstrated by modern physiology and clinical 
observation than this, that vital feebleness, in the great 
majority of instances, betrays itself by hurry of the vital 
motions ; and the first indication of returning strength is the 
return of a calmer and more equable rate of functional move- 
* Coleridge. 
o 
