1863.] 589 



induces great bubbling ; so that the pump cannot be used freely, for 

 fear of the froth overflowing. To this disturbance, involving the 

 exposure of successive portions of blood in the bubbles to the sides 

 of the vessel, I was inclined to attribute the more rapid coagulation ; 

 but in order to prove the point, I stirred for a few seconds the blood 

 in one of the vessels hitherto undisturbed. After eight minutes I 

 emptied the three vessels. I found that that blood which had not 

 been disturbed at all, either by the vacuum or by the rod, was still 

 almost entirely fluid, only showing a thin crust upon the glass and 

 on the surface exposed to the air. The blood which had been 

 subjected to the vacuum had a thick crust of clot on the surface, 

 and the sides of the glass were also thickly encrusted, but it still con- 

 tained a considerable quantity of fluid that could be poured out from 

 its interior. But that blood which had been stirred for only a few 

 seconds was a solid mass throughout. In other words, gentle stir- 

 ring of the blood for a few seconds had much greater effect in pro- 

 ducing coagulation than the protracted and efficient exhaustion which 

 was continued for upwards of 40 minutes, which was a considerable 

 time after all evolution of gas, as indicated by bubbles, had 

 ceased. 



Other experiments precisely similar in their effect were performed. 

 I therefore feel no hesitation in stating that the effects of a vacuum, 

 regarding which, indeed, the statements of different experimenters 

 have hitherto been conflicting, afford no evidence in favour of the 

 ammonia theory. 



There is another point of very great interest in the history of the 

 coagulation of the blood, which has been supposed to give support to 

 the ammonia theory ; and that is, the effect of temperature. It has 

 been long known that blood coagulates more rapidly at a high than 

 at a low temperature, and, indeed, a little above the freezing-point 

 remains entirely fluid. This seemed beautifully in harmony with the 

 ammonia theory, as heat would naturally promote, and cold retard 

 the evolution of the alkali, and a depression of temperature to near 

 the freezing-point might be reasonably supposed to prevent its escape 

 altogether. Indeed Dr. Richardson mentions as a fact, that ammonia 

 artificially mixed with blood ceases to be given off under such cir- 

 cumstances. 



