1863.] 583 



natural view was, that exposure to the air was the essential cause of 

 coagulation. Mr. Hewson believed that this was, at all events, an im- 

 portant element in the causes of the phenomenon ; and many emi- 

 nent physiologists and pathologists have held the same view, except 

 that, instead of the air as a whole, the oxygen of the air has been 

 supposed to be the important element 



Sir Charles Scudamore considered that coagulation was greatly 

 promoted by the escape of carbonic acid ; and more recently the evo- 

 lution of ammonia has been regarded as the essential cause of the 

 change. According to the ammonia theory, due to Dr. Richardson 

 of this city, the fluidity of the blood within the body depends on a 

 certain amount of free ammonia holding the fibrin in solution, and 

 the coagulation of the blood when withdrawn from the vessels is 

 the result of the escape of the volatile alkali. 



Then, as to vital theories. These have been held by many phy- 

 siologists, among whom may be mentioned Sir Astley Cooper and 

 Mr. Thackrah, who, from experiments which they performed, were 

 led to the inference that the living vessels exert an active influence 

 upon the blood, by which coagulation is prevented; and Mr. 

 Thackrah went so far as to attribute this action of the vessels to 

 nervous influence. The view that the blood is kept fluid by the 

 operation of its natural receptacles has been advocated more recently 

 by Briicke of Vienna, whose essay will be found in the ' British and 

 Foreign Medical Review' for 1857. Briicke performed his experi- 

 ments on turtles and frogs, in which animals the blood remains fluid 

 in the heart for days after death ; and I feel bound to say that some 

 of the facts which he has brought forward seem to me quite sufficient 

 to show that the ammonia theory, whatever amount of truth it may 

 contain, cannot be the whole truth, and cannot explain the fluidity 

 of the blood within the body. For example, Briicke found that, 

 having shed blood from the heart of a living turtle into a basin, 

 and transferred, with a syringe, a portion of that blood into the 

 empty heart of another turtle just killed, the blood thus transferred 

 into the empty heart remained fluid for hours ; whereas that which 

 was left in the basin coagulated in a few minutes. He also found 

 that blood continued fluid in the heart of a turtle long after the in- 

 jection of air into the heart through a vein till the cavities of the 

 organ contained a foamy mixture of blood and air. 



2x2 



