PHYSIOLOGY. 131 



others are only excited by particular artifices; so, taking the acid 

 of nitre in any degree of concentration, and applying it to quick- 

 silver, there will be an union ; but if I take the concentrated 

 acid of vitriol, and apply it to the quicksilver, in the present 

 state of the air, they will lie in contact without the least mark 

 of attraction, nor can the acid be made to act upon the mercury in 

 the cold ; but if you raise the temperature of the acid of vitriol to 

 the boiling point, it acts as the other, and here the cohesion is 

 increased or excited to a greater degree. These are some analogies 

 which may, in some measure, illustrate the matter, but there must 

 be a concurrent view, and a consideration of many other phenom- 

 ena, before we can apply it more strictly or specially to our nerv- 

 ous system ; and though I have thus thrown out a conjecture, 

 which, every time I take a view of the nervous system, seems to 

 me to approach nearer to probability, yet I do not say that it 

 will apply to the phenomena with any consistency."" 



CXXXI. This subject may be further illustrated, by ob- 

 serving that the excitement of the brain appears to be in very 

 different degrees on different occasions. It seems to be greatest 

 in certain maniacs endowed with uncommon strength, resisting 

 most impressions, and with the utmost difficulty admitting 

 sleep. " I say here, that the force or power producing excite- 

 ment is the strongest, because the animal power is in a con- 

 dition of resisting most powerfully all the causes that diminish 

 motion, as the causes of sleep ; so that I conclude from this, that 

 an extraordinary degree of the power of excitement takes place. 

 The fact is a matter of common observation : certain maniacs 

 are not only endowed with greater strength than others of a si- 

 milar condition are, but with vastly greater strength than they 

 have had themselves at other times. We are apt to conceive the 

 strength as residing in the muscles themselves, as a property be- 

 longing to them, but we not only cannot separate the considera- 

 tion of the exertion of animal power from that of muscular con- 

 traction, but this is in proportion to the volition, to the exertion 

 of animal power ; and an uncommon degree of strength must im- 

 ply an uncommon degree of excitement in the brain. I have 

 added another circumstance, which is that of resisting the force 

 of most impressions ; the fact is certain that maniacs are likewise 

 remarkable for resisting the power of impressions : thus, the 



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