116 ON THE COAGULATION OF THE BLOOD 
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 there- 
fore 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 circumstances. 
Though thinking it not unlikely that this was the true explanation 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 dis- 
tinctly acid reaction, the liquor sanguinis being of a colour that permitted the 
delicate 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, yet so long as it was kept in the cold it continued fluid, but when 
brought into a warm room 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. 
This experiment may not be satisfactory to all minds, though I confess 
it appears so to me; and, as this is a point of very great interest, I have sought 
in another way for evidence regarding it. First, however, I will mention an 
experiment which will not at once appear to bear on the question of temperature. 
I drew out a fine glass tube in such a way as to produce a fusiform receptacle 
continued longitudinally each way into a tube of almost capillary fineness for 
about two inches, which again expanded at the end, as represented in Fig. 3. 
Having squeezed out a drop of blood from my finger, I sucked up a portion 
into the tube till the receptacle A and its capillary extensions were filled. I then 
broke off the expanded ends, and placed the little tube thus filled, B, in a bath 
