544 PRACTICE OF PHYSIC. 



There are, perhaps, few disorders which act by paroxysms, that 

 do not depend on occasional causes ; and though the patient 

 may not observe these, they may be found out by diligent in- 

 quiry. To find out these is one of the most important things 

 in practice ; and they really exist always, though sometimes they 

 are very difficult to be discovered. This is very observable in 

 headach, where the slightest changes in diet, exercise, tem- 

 perature of the air, &c. are sufficient to bring on the disorder. We 

 can mark a great number of these occasional causes ; but it is 

 difficult to enumerate them, and still more to arrange them in 

 proper order. The first we shall mention is the plethora. This 

 is a frequent cause, and should, indeed, have been marked as a 

 predisposing cause, as it was in fact, when it was observed that 

 the disorder frequently prevailed in a sanguine habit. 



" We mention it here, because whatever increases it may be 

 an occasional cause of headach ; such as the fulness of diet, 

 j an obstruction in any evacuation, either natural, as menstru- 

 ! ation, &c. or spontaneous, as haemorrhagies at the nose, &c. 

 Thus headach generally prevails at the beginning of men- 

 struation. To this article of increased fulness in the body, we 

 may add costiveness, which often accompanies this disorder, and 

 when extended to a great degree may produce it. 



" Perhaps we may join here, cold applied to the extremities, 

 which, by the perspiration being obstructed, will excite fulness in 

 the vessels, and particularly in those of the head. Again, there 

 are other causes which act in producing a temporary turgescence 

 and rarefaction, such as being kept in any great degree of heat, 

 and particularly being exposed to a hot sun, &c. or a change 

 of weather from cold to hot, from heavy to light, and dry to 

 moist ; also, whatever increases the impetus of the blood, and 

 quickens the circulation, will have the same effect as a disten- 

 tion of the vessels, and may be an occasional cause. Such is 

 violent exercise, and some of the passions, particularly anger. 

 Those exercises too may be occasional causes which do not ex- 

 cite an impetus of the blood over the whole system, but stop 

 the reflux of the blood from the head, by preventing its free 

 passage through the lungs, and thereby causing a regurgita- 

 tion ; as much and loud speaking, violent laughter, coughing, 



