336 PRACTICE OF PHYSIC. 



will also be most likely to occur in persons of a corpulent habit, 

 either because these may be considered to be in a plethoric 

 state, or because obesity, by occasioning a compression of the 

 blood-vessels in other parts of the body, more readily fills 

 those of the brain, which are entirely free from any such compres- 

 sion. 



MCVTII. These are the circumstances in the constitution of 

 the body, which, producing a slower motion and return of the 

 venous blood from the vessels of the head, favour an accumula- 

 tion and distention in them ; and we now proceed to mention 

 the several occasional causes, which, in every person, may di- 

 rectly prevent the free return of the blood from the vessels of 

 the head towards the heart. Such are 



1. Stooping down with the head, or other situations of the 

 body in which the head is long kept in a depending state, and in 

 which the gravity of the blood increases the afflux of it by the 

 arteries, and opposes the return of it by the veins. -" I had oc- 

 casion to observe this very distinctly in a patient whom I had, 

 labouring under some hydropic symptoms ; and in whom a ste- 

 atomatous tumour pressed upon the branches of the aorta, with 

 constant flushing of the face, and other marks of fulness. In 

 several instances, stooping but for a little, brought on a short 

 apoplectic fit ; nay, he showed this in the way of experiment." 



2. A tight ligature about the neck, which compresses the 

 veins more strongly than the arteries. 



3. Any obstruction of a considerable number of the veins car- 

 rying the blood from the head, and more especially any consid- 

 erable obstruction of the ascending vena cava. 



4. Any considerable impediment of the free passage of the 

 blood from the veins into the right ventricle of the heart ; and 

 it is commonly by this, and the immediately preceding circum- 

 stance, that polypous concretions in the cava, or right ventricle, 

 are found to occasion apoplexy. 



5. The return of blood from the veins of the head towards 

 the heart, is especially interrupted by every circumstance that 

 produces a more difficult transmission of the blood through the 

 vessels of the lungs. It is well known, that, at the end of every 

 expiration, some interruption is given to the free transmission 

 of the blood through the lungs ; and that this at the same time 



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