COAGULATION OP THE BLOOD. 
757 
showing a thin crust upon the glass and on the surface ex¬ 
posed to the air. The blood ^Yhich 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 stirring of the blood for a few seconds 
had much greater effect in producing coagulation than the 
protracted and efficient exhaustion which was continued for 
upwards of forty 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 coagu¬ 
lates 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 circumstances. 
Though thinking it not unlikely that this was the true ex¬ 
planation of the influence of temperature on coagulation, I 
thought it worth while to subject the matter to experiment. 
For that purpose I kept the blood of a horse fluid by means 
of a freezing-mixture, and afterwards by ice-cold water; and 
when the corpuscles had subsided from the upper part of the 
blood, I cautiously added to the liquor sanguinis extremely 
dilute ice-cold acetic acid till it was of distinctly acid reaction, 
the liquor sanguinis being of a colour that permitted the de¬ 
licate application of test-paper, which is impossible with red 
blood. By this means any free ammonia which the fluid 
might have contained must have been neutralized; vet so 
long as it was kept in the cold it continued fluid, but when 
brought into a warm room it coagulated just as a specimen 
which had not been acidulated. Thus, when there could be 
no free ammonia in the liquor sanguinis at all, it was still 
affected as usual by temperature. 
