STAGGERS, &c. 311 



" and this either proceeds from a caufe with- 

 *^ out the veflels, viz. when the blood or any 

 " other fluid happens to break out of fome 

 " veffel within the brain, or when there hap- 

 ** pens to be preternatural bones or tumours 

 ^* bred and contained within the Ikull, or 

 " any other extraneous matter that may, in 

 " any fort, prefs upon the foft fubftance of the 

 ** brain, cauling thofe deadly diforders. ' But 

 " this is a fpecies that is incurable, and, for 

 ** the moft part, feizes fuddenly, without any 

 ** foregoing tokens or warnings. Thus in an 

 ** APOPLEXY fenfe and motion are in a m.anner 

 " quite loft, becaufe of the preffure that is 

 ** made upon the origin of all the nerves that 

 *^ arife from the head: but, in a vertigo, 

 *^ objedts that are at reft appear as if they 

 ** were turning round, and by that means 

 ** occafion any creature to reel and ftagger ; 

 *' and this proceeds from the vibrations and 

 ** tremors of the optic nerve, whereby the 

 ** images falling not diredtly but fucceffively 

 " upon the different parts of the retina^ an 

 ** objeft that is at reft will therefore appear 

 *^ as if turning round ; and this may be occa- 

 *' fioned either when an animal is fearful of 

 ** falling, or from a repletion or overfulnefs 



X 4 - of 



