CATJSE OF COAGULATION OF THE BLOOD. 163 



" After the leech was removed from the arm, the wound 

 it had produced continued to give out blood very freely. I 

 caught the blood thus flowing at different intervals, allowing 

 it to trickle into teaspoons of the same size and shape. The 

 results were curious. The blood which was received into the 

 first spoon, and which was collected immediately after the 

 removal of the leech, was dark, and showed the same feeble- 

 ness of coagulation as the blood taken from the leech itself. 

 Another portion of blood, received into a second spoon five 

 minutes later, coagulated in twenty-five minutes with mod- 

 erate firmness. A third portion of blood, caught ten min- 

 utes later still, coagulated in eight minutes ; while at the 

 end of half an hour the blood which still flowed from the 

 wound coagulated firmly, and in fine red clots, in two min- 

 utes. Ultimately the blood coagulated as it slowly oozed 

 from the wound, so that the wound itself was sealed up." l 



The existence of projections into the caliber of vessels, 

 or, as was done by Simon, the passage of a fine thread through 

 an artery or vein, will determine the formation of a small 

 coagulum upon the foreign substance, while the circulation 

 is neither interrupted nor retarded. These facts demand 

 explanation, but all we can say with regard to them is, that 

 in the present state of our knowledge explanation is difficult, 

 if not impossible. As before remarked, the process, under 

 these circumstances, cannot be subjected to direct experiment, 

 as in the case of the blood coagulating out of the body. 



Since the publication of Richardson's essay, various 

 experiments 011 coagulation out of the body have been made 

 which are claimed to disprove his views. Dr. John Davy 

 has reported some experiments on the coagulation of blood 

 in the common fowl, in which he attempts to show that the 

 process is not attended with the evolution of ammonia, and 

 furthermore, that ammonia mixed with the blood will not 

 prevent coagulation. 2 It is well known that the blood of 



1 Op. eit., p. 207. 



2 JOHN DAVY, M.D., Physiological Researches, London, 1863, p. 384 et seq. 



