338 PRACTICE OF PHYSIC. 



causes (MCV. MCVIII.) of a preternatural fulness in the 

 blood-vessels of the brain, may produce apoplexy in different 

 ways, according as the fulness takes place in the arteries or in 

 the veins. 



MCX. Accordingly, first, The increased afflux of blood in- 

 to the arteries of the brain, and an increased action in these, 

 may either occasion a rupture of their extremities, and thereby 

 an effusion of red blood producing compression ; or the same 

 afflux and increased action may occasion an increased exhalation 

 from their extremities, of a serous fluid, which, if not as quickly 

 re-absorbed, may soon accumulate in such a quantity as to 

 produce compression. 



MCXI. Secondly, The plethoric state of the venous vessels 

 of the brain may operate in three different ways. 



1. The fulness of the veins may give such resistance to the 

 blood flowing into them from the arteries, as to determine the 

 impetus of the blood to be so much greater upon the extremi- 

 ties of the arteries as to occasion a rupture of these, and conse- 

 quently an effusion of red blood, or the Hcemorrhagia cerebri, 

 which Hoffmann considers as a frequent cause of apoplexy, and 

 which we have before explained in DCCLXXII. 



2. Whilst the same resistance to the blood flowing from the 

 arteries into the veins increases the impetus of the blood in the 

 former, this may, without occasioning rupture, increase the 

 exhalation from their exhalent extremities, and produce an 

 effusion of a serous fluid ; in the same manner, as such resist- 

 ance in the veins produces hydropic effusions in other parts of 

 the body. 



3. If we may suppose, as no lymphatics have been yet 

 discovered in the brain, that the ordinary absorbents are not 

 present there, and that the exhaled fluids are absorbed or taken 

 up by the extremities of the veins ; this will show still more 

 clearly that a resistance to the motion of the blood in the veins 

 of the brain may readily produce an accumulation of serous 

 fluid in its cavities, and consequently a compression producing 

 apoplexy. 



MCXI I. Besides these cases of apoplexy from afflux in the 

 arteries, or resistance in the veins, an effusion of serum may 

 happen from two other causes, The one is a relaxation of the 



