ADYNAMIJE. 365 



the ligature which had been employed is untied, and admits a 

 larger afflux of blood into the blood-vessels of the arm. Both 

 these cases of syncope show that an evacuation of blood does 

 not always occasion the disease by any general effect on the 

 whole system, but often merely by taking off the requisite full- 

 ness of the blood-vessels of the brain. 



MCLXXVIII. The operation of some others of the remote 

 causes of syncope may be explained on the following principles. 

 Whilst the energy of the brain is, upon different occasions, 

 manifestly stronger or weaker, it seems to be with this condi- 

 tion, that a stronger exertion of it is necessarily followed by a 

 weaker state of the same. It seems to depend upon this law in 

 the constitution of the nervous power, that the ordinary contrac- 

 tion of a muscle is always alternated with a relaxation of the 

 same ; that, unless a contraction proceeds to the degree of 

 spasm, the contracted state cannot be long continued : and it 

 seems to depend upon the same cause that the voluntary mo- 

 tions, which always require an unusual increase of exertion, oc- 

 casion fatigue, debility, and at length irresistible sleep. 



From this law, therefore, of the nervous power, we may un- 

 derstand why a sudden and violent exertion of the energy of 

 the brain is sometimes followed by such a diminution of it as to 

 occasion a syncope ; and it is thus, I suppose, that a violent fit 

 of joy produces syncope, and even death. It is upon the same 

 principle also, I suppose, that an exquisite pain may sometimes 

 excite the energy of the brain more strongly than can be sup- 

 ported, and is therefore followed by such a diminution as must 

 occasion fainting. But the effect of this principle appears more 

 clearly in this, that a fainting readily happens upon the sudden 

 remission of a considerable pain ; and thus I have seen a faint- 

 ing occur upon the reduction of a painful dislocation. 



MCLXXIX. It seems to be quite analogous when a syn- 

 cope immediately happens on the finishing of any great and 

 long-continued effort, whether depending on the will, or upon a 

 propensity ; and, in this way, a fainting sometimes happens to 

 a woman on the bearing of a child. This may be well illustrat- 

 ed by observing, that, in persons already much weakened, even 

 a very moderate effort will sometimes occasion fainting. 



MCLXXX. To explain the operation of some other causes 



