HE AD AC II. 541 



certain, and its producing external pain, is probable both in fact 

 and from reason. We have given some means of discerning 

 when such causes take place, and we proceed to consider where- 

 in they consist. 



" For this we must look into the histories of dissections, and 

 there we find all the same circumstances which we found in the 

 cases of epilepsy ; viz. Ossified meninges, Collections of acrid 

 matter, Indolent tumours, Turgid blood-vessels, Effusions of 

 blood, Effusions of serum. 



" From all this we may draw the same conclusions that we 

 did with respect to epilepsy. But there may be some difficulty. 

 It may be alleged, that such appearances in the cases of head- 

 ach, which were followed by epilepsy, were to be expected as 

 in epilepsy ; but that does not prove that they existed in the 

 preceding headach. Perhaps not certainly ; but let us ex- 

 amine ; and, first, it is remarkable, that headach changes into 

 most of the diseases of the head. 



" In the cases of headach (above one hundred) mentioned by 

 Lieutaud, there are the clearest proofs of this : There are twenty- 

 five cases changing into lethargy, palsy, and apoplexy ; twenty, 

 into epilepsy and convulsions ; as many into all the different 

 kinds of vesanioc. These are a great part of the whole, and 

 many of the rest are instances to the same purpose. 



" From this we form several conclusions : From their com- 

 mon connexion with headach, it appears that the other diseases 

 have a connexion with each other ; especially from hence, that 

 so many thus connected shew the same appearances upon dis- 

 section. 



" There is little doubt with respect to the headachs that pre- 

 ceded these diseases. If the latter are supposed to shew an ef- 

 fusion of blood, there will be little doubt that their lesser degrees 

 depended on like causes in a less degree, upon turgescence and 

 increased impetus ; and therefore that the headach depended 

 upon the same. 



" The conclusion, upon the whole, is, that the principal dis- 

 eases of the head, and the headach so generally connected with 

 them, depend commonly and frequently upon the change of the 

 state of the circulation in the vessels of the head. This is par- 

 ticularly confirmed with respect to headach by the consider- 





