OF THE VEINS. 



347 



m. 



It appears, further, that if the veins were rigid, 

 or placed in circumstances where their sides re- 

 mained apart when wounded, instead of blood 

 escaping, air might be drawn into them through 

 the expansion of the chest in breathing — and this 

 is a most important circumstance ; for when such 

 an accident takes place, death follows instanta- 

 neously. When a reservoir is emptied by a per- 

 pendicular tube, into which a smaller tube is 

 inserted, the water descending by the larger tube 

 instead of escaping by the lesser, will draw the 

 water up through that lesser tube so as to empty 

 the glass in which its lower end is immersed. By 

 this we see that there may be points on the sides 

 of tubes conveying fluid, in which the pressure 

 may be negative ; and we are made aware that 



