COMATA. 337 



gives an interruption to the motion of the blood from the veins 

 into the right ventricle of the heart. This clearly appears from 

 that regurgitation of the blood in the veins which occasions the 

 alternate heaving and subsiding that is perceived in the brain 

 of Jiving animals when the cranium is removed, and which is 

 observed to be synchronous with the alternate motions of respi- 

 ration. From this, we readily perceive, that whatever occasions 

 a difficulty in the transmission of the blood through the lungs, 

 must also interrupt the free return of the venous blood from 

 the vessels of the head, and must therefore favour, s id perhaps 

 produce, an accumulation of blood, and an over-distention in 

 these vessels. 



It is further to be observed, that, as a very full inspiration, 

 continued for any length of time, occasions such an interruption 

 of the free transmission of the blood through the lungs, as pro- 

 duces a suffusion of face, and a manifest turgescence of the blood- 

 vessels of the head and neck; so every full and long-continued in- 

 spiration IB ay occasion an accumulation of blood in the vessels of 

 the head, to a very considerable degree. Thus, as every strong ex- 

 ertion of the muscular force of the body requires, and is attend- 

 ed with a very full and long-continued inspiration, we thence 

 learn why the violent exertions of muscular force have been so 

 often the immediate or exciting causes of apoplexy. 



It may also be remarked, that corpulency and obesity seem 

 to operate very much, by occasioning a more difficult transmis- 

 sion of the blood through the vessels of the lungs. It appears 

 that, in fat persons, from the compression of the blood-vessels 

 in many parts of the body, the vessels of the lungs are thereby 

 cept very full; so that, upon the least increase of bodily motion, 

 which sends the blood faster into the lungs, a more frequent and 

 laborious respiration becomes in such persons immediately ne- 

 cessary. This shows, that, in such persons, the blood is not 

 freely transmitted through the lungs ; a circumstance which, as 

 in other instances, must give a constant resistance to the return 

 of blood from the vessels of the head, and therefore favour or 

 occasion an accumulation of blood in them. 



Is the motion of the blood in the vessels of the head rendered 

 slower by study, care, and anxiety ? 



MCIX. It is to be observed further, that these several 



VOL. II. Y 



