212 ON THE NATURE AND PRINCIPLES OF 



mination, and which has been occasionally tried with 

 success in this affection of the cerebral arteries, ac- 

 complishes directly what derivatives can only effect 

 secondarily, namely, a diminution of the pressure 

 acting upon the affected vessels. Its general im- 

 practicability is the only argument against its uni- 

 versal adoption. 



The second indication in the treatment of this 

 disorder is, to assist the arteries as much as possible 

 in their reaction. In most cases we can only indi- 

 rectly promote this salutary effort by withdrawing 

 the distending force ; but in determination to the 

 head, the application of cold to the surface is found 

 to exercise a direct action in favouring the contrac- 

 tion of the enlarged vessels. The influence of this 

 agent is not confined to the capillaries ; it is capable 

 of diminishing the calibre of arteries of considerable 

 size, whether immediately applied to them, or pro- 

 pagating its influence along the coats of the smaller 

 vessels. 



I have now endeavoured to trace the morbid 

 effects resulting from an obstruction to the blood's 

 passage through the different parts of the circulating 

 system. 



Venous obstruction is important chiefly from its 

 lisordering the capillary circulation. And such is 

 the admirable arrangement adopted by nature for 

 the prevention of this occurrence, that there arc 

 very few parts in which the closure of one vein will 

 completely arrest, or even materially disturb, the 

 circulation through the capillaries. 



The importance of these disorders of the circulation 



