540 PRACTICE OF PHYSIC. 



from the other three, inflammatory, chemical, and spasmodic. 

 It may depend upon their action, but the pain is produced in a 

 different manner, and leads to a different diagnostic. This 

 leads to 



" The second difficulty in the case of headach : which is, 

 that in headach, also, it is doubtful if we may conclude from the 

 seat of the pain as to the seat of the disease whether it be ex- 

 ternal or internal, or partly the one and partly the other. 



" We may conclude that it depends on an internal affection, 

 when, although the pain is referred to an external part, that part 

 is not affected by any external pressure. When it is, we ac- 

 knowledge an external affection, but we must not immediately 

 conclude that this is the whole, and that there is no internal 

 disease. We know that it is often otherwise. 



" Lieutaud mentions above one hundred cases of external 

 headach, in every one of which on dissection an internal 

 affection was found ; and here is the difficulty. It may 

 be supposed that the external was primary, arid the internal 

 its consequence, as well as that the contrary may happen. 

 But without stopping to shew the improbability of the first sup- 

 position, we have other and surer means of determining that an 

 internal affection at least concurs with the external in many cases. 

 These are the presence of symptoms of an affection of the brain, 

 or origin of the nerves : as vertigo, stupor, oblivion, delirium. 

 To these I add, blindness, deafness, loss of smell. These last 

 are indeed ambiguous, and may depend on an external affection 

 of the respective organs ; but when joined with the former, which 

 establish an internal affection, it is probable, that both depend 

 on the same cause. 



" But in many cases we are certain, that the internal is the 

 primary affection, because the exciting cause is such as must 

 first act there. Such are the passions of the mind ; my own 

 case. If anger or shame produce a suffusion of the face, there 

 is no doubt that this is communicated from the brain ; and let 

 it be remarked by the way, that however difficult it may be to 

 explain the manner, these and other expressions of the passions 

 are certain proofs of a communication between the brain and the 

 external parts of the head. 



" From the whole of this, the evidence of an internal cause is 



