THE BLOOD. 483 



" I may remind the Fellows of this Society, that in a paper which I 

 had the honour to read before them the Session before last,* I brought 

 forward facts which seemed to prove that the ammonia theory does not 

 apply to blood within the vessels of a living animal. That theory, as 

 my hearers are doubtless aware, asserts that the fluidity of the blood 

 depends upon the presence of a certain amount of free ammonia hold- 

 ing the fibrine in solution, and that coagulation is the necessary result 

 of the escape of the volatile alkali. But it was shown in the paper 

 referred to, that the blood, in man and other mammalia, though coagu- 

 lating soon after death in the heart and great venous trunks, remains 

 fluid for days in vessels of smaller size, and this under circumstances 

 affording free opportunity for the escape of ammonia ; and, on the 

 other hand, that when a portion of a vessel either in an amputated 

 limb or in a living animal is treated in a manner calculated to destroy 

 its vital properties, the blood coagulates in the injured part, but retains 

 its fluidity elsewhere, although there is no greater opportunity for the 

 escape of ammonia in the one case than in the other. A striking 

 instance of the difference between the natural receptacles of the blood 

 and ordinary matter in their relations to the vital fluid happened to 

 come under my notice this morning, in an arm which I amputated last 

 evening at the shoulder-joint, on account of injury inflicted by machi- 

 nery. On examining the limb, which had lain undisturbed since the 

 operation, I saw that the axillary vein, which was patulous at the part 

 where it had been divided by the knife, contained some blood at a 

 distance of about half-an-inch from the open orifice ; and having 

 squeezed out a few drops, found that it was perfectly fluid, but yielded 

 threads of fibrine when the point of a needle was drawn through it 

 some minutes after emission. The blood had been for upwards of 

 twelve hours freely exposed to the air, but being situated in an unin- 

 jured part of a blood-vessel, had remained free from coagulation. 



"Further, in the opening meeting of last Session I demonstrated 

 another important principle, viz. That ordinary solid matter, unlike 

 atmospheric air, induces coagulation of blood in its vicinity when in- 

 troduced within the living vessels. Having inserted a piece of clean 

 silver wire for a considerable distance into one of the veins of an am- 

 putated sheep's foot, I slit up the vessel after a short time had elapsed 

 when I exhibited a coagulum extending along the whole length of the 

 foreign body, whereas a mere wound of the vein failed to induce a clot 

 * Vide Edinburgh Medical Journal, April 1858. 



