588 [June 11, 



tunity of parting with its ammonia, coagulated much more rapidly 

 than that in an open vessel. The difference between the two was, 

 that the lower portion of the blood had been freely exposed to the 

 influence of the foreign solid, whereas the other had only been sub- 

 jected to the action of the wall of the tube. 



The same principle may be illustrated by an exceedingly simple 

 experiment which I performed only this very day. Receiving blood 

 from the throat of a bullock into two similar wide-mouthed bottles, 

 I immediately stirred one of them with a clean ivory rod for 10 

 seconds very gently, so as to avoid the introduction of any air, and 

 then left both undisturbed. At the end of a certain number of 

 minutes I found that, while the blood which had not been disturbed 

 could be poured out as a fluid, with the exception of a thin layer of 

 clot on the surface, and an incrustation on the interior of the vessel, 

 the blood in the other vessel, which had been stirred for so brief a 

 period, was already a solid mass. 



I have only lately been aware of the great influence exerted upon 

 the blood by exposure for a very short time to a foreign solid, 

 and I feel that many of my own experiments, and many performed 

 by others, have been vitiated for want of this knowledge. Take, for 

 example, the effect of a vacuum, which was observed by Sir Charles 

 Scudamore to promote coagulation. This has been considered by 

 Dr. Richardson as an illustration of his theory, the vacuum being sup- 

 posed to act by favouring the escape of ammonia. I have lately 

 inquired into this subject, and I feel no doubt whatever that the 

 greater rapidity of coagulation in a vacuum depends simply on the 

 greater disturbance of the fluid. I made the following experiment : 

 I filled three bottles, such as these, from the throat of a bullock, 

 placed one of them under the small bell jar of an air-pump in good 

 order and exhausted it, leaving the other two undisturbed. The 

 blood happened to be slow in coagulating ; and at the end of about 

 forty minutes, in the vessels where the blood had been undisturbed, 

 there was only a slight film of coagulum on the surface, whereas the 

 blood under the vacuum was found on examination to have a very 

 thick crust of clot upon it. But during the process of exhaustion 

 the blood had bubbled very much. Indeed, any exhaustion of blood 

 recently drawn which is sufficient to cause the evolution of its gases 



