600 [June 11, 



tween the blood and the side of the glass and make a slight rotatory 

 movement of the handle, you see through the glass the point of the 

 needle detaching a layer of clot whatever part you may examine. 

 The process of coagulation having thus commenced in contact with 

 the surface of the vessel into which the blood is shed, may under 

 favourable circumstances be ascertained to travel inwards, like ad- 

 vancing crystallization, towards the centre of the mass. It appears, 

 however, that this extension of the coagulating process would not 

 take place had not the blood been prepared for the change by 

 contact, during the process of shedding, with the injured orifice 

 of the blood-vessel and with the surface of the receptacle. I have 

 only very recently become acquainted with the remarkable subtlety 

 of the influence exerted upon blood by ordinary solids. I was long 

 since struck with the fact, that if I introduced the point of an 

 ordinary sewing-needle through the wall of a vein in a sheep's 

 foot and left it for twelve hours undisturbed, the clot was still 

 confined to a crust round the point of the needle, implying that 

 coagulum has only a very limited power of extension. I thought, 

 therefore, that by proper management it might be possible to 

 keep blood fluid in a vessel of ordinary solid matter lined with 

 clot. But various attempts made with this object failed entirely, till 

 I lately adopted the following expedient. Having opened the distal 

 end of an ox's jugular vein containing blood and held in the vertical 

 position, taking care to avoid contact of any of the blood with the 

 wounded edge of the vessel, I slipped steadily down into it a cylin- 

 drical tube of thin glass, somewhat smaller in diameter than the vein, 

 open at both ends, and with the lower edge ground smooth in order 

 that it might pass readily over the lining membrane, and so disturb 

 the blood as little as possible by its introduction, and influence only 

 the circumferential parts of its contents. The tube was then kept 

 pressed down vertically upon the bottom of the vein by a weight, in 

 a room as free as possible from vibration, and I found on examining 

 it at the end of twelve hours that the clot was a tubular one, consist- 

 ing of a crust about one-eighth of an inch thick next the glass and 

 the part exposed to the air, but containing in its interior fluid and 

 rapidly coagulable blood. In another such experiment, continued for 

 twenty-fours, though the crust of clot was thicker, the central part 

 still furnished coagulable blood. 



