538 PRACTICE OF PHYSIC. 



Cephalaea arthritica, febricosa, Polonica ; Haemicrania coryzse, 

 haemorrhoidalis, nephralgica ; and I think, on the same ground, 

 the Cephalalgia hysterica, Cephalaea melancholica, Hemicrania 

 clavus, and lunatica. 



" 3. The Cephalalgia anemotropa, as taken from a cause that 

 does not vary the disease, 



" The whole species of Sauvages are thus rejected, except 

 three, Cephalalgiaplethorica (sp. 1.), Cephalaea serosa (sp 7-)> 

 and Cephala^ia metallica (sp. 13.), which I am disposed to 

 reject altogether. 



" Besides these, the rest are all symptomatic, but there are 

 idiopathic species not at all mentioned by Sauvages. We have 

 endeavoured to shew that the principal species of idiopathic 

 headach may be considered as a topical fever. 



" We are now to treat of headach as a symptonronly, this 

 being necessary previous to any consideration of it as a disease. 

 But the subject is difficult, and I think it proper to state the 

 difficulties. 



" Thejirst arises from the theory of pain in general. Many 

 causes of pain manifestly have a tendency to destroy the con- 

 tinuity of the nervous substance, as violent distention, tight lig- 

 atures, and cutting instruments. Chemical impression is often 

 of the same kind, as for example, that of the most powerful sol- 

 vents. This has produced a notion, that pain always depends 

 on an impulse approaching to a solution of continuity. But 

 Dr. Haller and others have observed, that this is not universal- 

 ly the case ; and it is obvious that impulses, far short of this, 

 produce pain ; and this occurs where an increase of impulse pro- 

 duces a strong sensation of impression. We are still therefore 

 to seek for an increase of impulse or motion in the part in every 

 case of pain. 



" In all cases of pain arising from an external cause we are at 

 no loss to find the increase of motion, but in those in which the 

 cause is internal, it is not always obvious. In these we, in the 

 first place, suspect the distention of vessels produced by an in- 

 creased impetus of the fluids, an inflammatory congestion ; and 

 this is a frequent cause of pain, both by itself and in combina- 

 tion with other causes ; it frequently exists where it is little ob- 

 served, as it is often topical. 



