HEADACII. 553 



indeed appear sometimes in fits of a topical fever ; but such 

 instances are very rare. Its occasional causes may perhaps be 

 referred to these two heads, 1. Such as hinder the reflux of the 

 venous blood from the vessels of the head, as stooping, &c. 

 2. Whatever weakens the system, and diminishes the impetus 

 of the nervous power. Thus melancholy, hypochondriasis, and 

 such others, will excite occasional fits of this headach, for it is 

 seldom periodical. What is its particular nature has not been 

 determined. 



" Another of these species of headachs, which cannot easily 

 be referred to the principal idiopathic, is that connected with 

 the menstrual or haemorrhoidal flux, and called Cephalalgia 

 catamenialis and hcemorrhoidalis. The coming on of the 

 hoemorrhoidal flux is not exactly periodical, and is often fore- 

 told by this headach. The notion which would most readily 

 occur here is, that the plethora is owing to some resistance 

 made to the blood, as it endeavours to pass off by these vessels, 

 whereby it is made to regurgitate on the brain. But this is liable 

 to many difficulties ; and all the arguments which, in the ques- 

 tion, Whether the plethora of the menstrual flux is universal or 

 topical, have been brought against an universal plethora, will 

 apply here. Still, however, the menstrual and haemorrhoidal 

 flux are to be looked upon as topical fevers, founded on a turgid 

 state of the vessels of the uterus and anus : even a moderate tur- 

 gescence here, without a plethora of the other vessels, may excite 

 a painful tension in other parts of the system, and promote the 

 impetus in them ; and it accordingly does so. Thus, when the 

 menstrual flux is obstructed, it is sometimes determined to the 

 lungs, sometimes to the stomach, and may easily be so to the 

 head, independently of any general plethora of the system. 

 There is, indeed, either something particular in the vessels 

 of the head, or it is in consequence of its communication with 

 the sensorium commune, that the head is so much affected in 

 all fevers. But why it is so, has not been yet fully solved. 

 Taking the catamenial and haemorrhoidal headachs, then, in 

 this view, as topical fevers, we may observe, that there is a 

 headach, which often follows these discharges, when they have 

 been remarkably plentiful. This, then, cannot be of the ple- 

 thoric kind, but of the constricting. 



