IS COAGULATION A PHYSICAL ACT? 725 



bumen, it is known, is rendered soluble by the fixed alkali, soda, but 

 may be precipitated by the addition of an acid. Lastly, it has been 

 shown, by Richardson, that ammonia is really given off from blood, 

 microscopic crystals of hydrochlorate of ammonia being formed on a 

 piece of glass moistened with a trace of hydrochloric acid, and held 

 over freshly-drawn blood ; also that, by the transmission of the am- 

 moniacal vapor from fresh blood, through other fresh blood, the latter 

 may be kept fluid for an unusual time ; that air containing the vapor 

 of ammonia has the same effect, and will, even after coagulation has 

 taken place, restore the condition of fluidity the clotted and fluid 

 conditions being alternately producible, according as the ammoniacal 

 vapor is passed into the blood, or is permitted to escape from it. The 

 minute proportion of 1 part of ammonia to 3000 of blood, is sufficient 

 to maintain the fluidity of the latter. Finally, nearly all the condi- 

 tions which appear to favor or accelerate the coagulation of freshly- 

 drawn blood, are such as would also facilitate the escape of the vola- 

 tile alkali from it (Richardson). 



Other considerations and facts appear, however, to show that the 

 escape of the ammonia from the blood, which undoubtedly occurs, is 

 not the cause of the solidification of the fibrin, but merely an accom- 

 paniment of that change. In the liquefaction of solid fibrin by am- 

 monia, and its alternate re-coagulation and liquefaction by the subse- 

 quent subtraction and addition of ammonia, it is not certain whether 

 the fibrin of these secondary and tertiary solidifications is identical 

 with the fibrin of the primary clot. Many experiments and observa- 

 tions further show that freshly-drawn blood may be placed in such con- 

 ditions that its ammonia cannot well escape, and yet coagulation will 

 occur; e. g., when blood is received into a bottle which is quickly 

 stoppered, or when blood rendered fluid by ammonia coagulates, though 

 tardily, if kept in air-tight vessels (Zimmerman) ; or, again, when 

 blood, subjected to increased barometric pressure, which would check 

 or prevent the escape of ammonia, is found to coagulate even quicker 

 than usual (Colin). Moreover, blood drawn from an animal, and ex- 

 posed to the air for fifteen minutes, at a temperature of 32, even 

 though its ammonia had probably escaped, has been found to remain 

 fluid for upwards of five hours, when introduced into the freshly re- 

 moved heart (Briicke). The blood in a dead body is usually found 

 coagulated in the heart and the larger arteries and veins, but fluid in 

 the smaller vessels, although ammonia could apparently escape or 

 transude more easily from the latter. This coagulation in the heart 

 and larger vessels, is partly due to post-mortem changes, but, some- 

 times at least, the clots begin to form during the last moments of life. 

 Again, blood confined between two ligatures in a living vein, retains 

 its fluidity for many hours ; but if a piece of glass-tube be introduced 

 between the blood and the walls of the vein, coagulation very speedily 

 occurs (Briicke). So, too, when needles, wires, or threads are passed 

 through living vessels, the blood will coagulate in the vessels, though 

 the ammonia could not, by any possibility, escape from the moving 

 blood (Simon and Lister). The coagula thus formed in veins, are 

 large, soft, and dark; whilst those formed in pierced arteries are 



