Page:The third Huxley lecture.pdf/50

46 a vein occasioned coagulation in its vicinity. The end of a sewing needle pushed through the wall of a vein otherwise uninjured, became after a while encrusted with a layer of fibrin deposited upon the part within the vessel, while the rest of the blood in it retained its fluidity. On the other hand, having injected air into the vessels on another occasion, I found seven hours later that their contents were a frothy mixture of blood and air, the walls of whose bubbles were fluid, but solidified when shed. Sir Astley Cooper had been of opinion that the living vessels kept the blood within them fluid by acting in some way upon it—in other words, his view implied that the blood had a spontaneous tendency to coagulate, which was held in check by the active operation of the living tubes that contained it. Facts such as I have just mentioned seemed to me to indicate that the ordinary solid was the active agent: determining the formation of fibrin as a thread does the deposition of sugar candy; while the healthy living tissue had the