212 PRACTICE OF PHYSIC. 



the proportional quantities of the blood in the arteries and veins, 

 it must be evident that the plethoric state of the arteries will be 

 in a great measure taken off; and, therefore, that the arterial 

 haemorrhagy is no longer likely to happen ; but that, if a general 

 plethoric state afterwards take place in the system, it must es- 

 pecially appear in the veins. 



DCCLXVII. The change I have mentioned to happen in 

 the state of the arterial and venous systems, is properly sup- 

 posed to take place in the human body about the age of thirty- 

 five, when it is manifest that the vigour of the body, which de- 

 pends so much upon the fulness and tension of the arterial sys- 

 tem, no longer increases ; and therefore it is, that the same age 

 is the period, after which the arterial haemorrhagy, haemoptysis, 

 hardly every appears. It is true, there are instances of the 

 haemoptysis happening at a later period ; but it is for the reasons 

 given (DCCLVIIL), which show that an haemorrhagy may 

 happen at any period of life, from accidental causes forming 

 congestions, independent of the state of the balance of the sys- 

 tem at that particular period. 



DCCLXVIII. I have said (DCCLXVL), that if, after the 

 age of thirty-five, a general and preternatural plethoric state oc- 

 cur, it must especially appear in the venous system ; and I must 

 now observe, that this venous plethora may also give occasion to 

 haemorrhagy. 



DCCLXIX. If a plethoric state of the venous system take 

 place, it is to be presumed, that it will especially and in the first 

 place affect the system of the vena portarum, in which the mo- 

 tion of the venous blood is more slow than elsewhere ; in which 

 the motion of the blood is little assisted by external compression ; 

 and in which, from the want of valves in the veins that form the 

 vena portarum, the motion of the blood is little assisted by the 

 compression that is applied ; while, from the same want of valves 

 in those veins, the blood is more ready to regurgitate in them. 

 Whether any regurgitation of the blood can produce an action 

 in the veins, and which inverted, or directed towards their ex- 

 tremities, can force these, and occasion haemorrhagy, may per- 

 haps be disputed : but it appears to me that an haemorrhagy, 

 produced by a plethoric state of the veins, may be explained in 

 another and more probable manner. If the blood be accumu- 



