VENESECTION 



697 



ing to the quantity of blood withdrawn, but the bloodvessels 

 quickly adjust themselves to the smaller mass of blood, and 

 the original quantity of this vital fluid is soon restored (24 

 to 48 hours) through absorption from the tissues and ali- 

 mentary canal. The heart beats more rapidly, owing to the 

 lessened resistance in the vessels, and venesection is accom- 

 panied by nausea and prostration. 



The blood is less dense and more fluid after blood- 

 letting, and for this reason, if inflammatory processes follow, 

 exudation is more apt to ensue. The fibrin is first regained, 

 then the normal number of white, and finally that of red 

 corpuscles, in from one to five weeks. Circulatory depress- 

 ants — as veratrum viride — accomplish much the same results 

 as blood-letting, by causing general reduction of vascular 

 tension and relief from local congestion, thus " bleeding an 

 animal into its own veins " without loss of blood, it is true, 

 but with less rapid and certain effect. 



Cathartics, diuretics and diarphoretics also lower blood 

 pressure by abstraction of fluid from the vessels, but their 

 action is slow. The following disorders are those most 

 suitable for treatment by venesection when they exist in an 

 alarming form in robust animals : 



Sthenic pneumonia. 

 Sthenic pleuritis. 

 Urticaria. 

 Lymphangitis. 



( Bacterial, 

 Toxaemia < Mineral, 



( Vegetable. 

 (Followed by saline infusion.) 



Cerebral congestion. In insolation 



and tympanitis. 

 Apoplexy, particularly parturient 



apoplexy of cows. 

 Encephalitis. 



Acute cerebral meningitis. 

 Active pulmonary congestion and 



apoplexy. 

 Passive pulmonary congestion in 



cardiac disease. 



Venesection from the jugular in cerebral congestion is, 

 in fact, a species of local blood-letting by directly draining 

 blood away from the brain; and it preserves life by pre- 

 venting pressure od, and paralysis of, the great vital medul- 

 lary centres controlling the respiration and heart. Moderate 

 blood-letting is sometimes advisable in the early stages of 



