The Coai^ulatioii Time of the Blood in Man 311 



37 (J. Ill the 10 seconds or so which are required to place it in the oil, 

 the temperature falls; and it continues to fall until it reaches 185^0., the 

 temperature of the oil, after which it remains constant. 



As variability of temperature is the most important source of fallacy in 

 other methods, so its constancy is the chief advantage in this one. This 

 is the one reason why the results are so much more constant than can be 

 obtained by other methods. Another point which may be looked \ipou 

 as a special advantage is that coagulation occurs under c(mditions not 

 very dissiuiilar to those which obtain in an injured vessel, or one into which 

 a foreign body has been introduced. . In both cases the blood is flowing, 

 and thrombokinase from the tissues has been added to it. In the one case 

 it is surrounded by the vascular endothelium, and in the other case by oil 

 which in its neutrality as regards (!oagulati(jn is strictly comparable to the 

 lining of the vessels.^ 



Coagulation may, therefore, be said to occur under conditions much 

 more nearly allied to those under which blood sometimes coagulates within 

 the body than when observed by any method hitherto employed. Never- 

 theless the method here described is far from being a perfect one. This 

 is shown by the fact that irregular variations in the time of coagulation 

 still occur even with a constant temperature. These variations are not 

 due to alterations in the actual coagulability of the blood, but must, I think, 

 l)e attributed to experimental error. 



They appear to be due to two causes — first, slight errors in techniipu'. 

 and second, a want of absolute detiniteness in the end-point. 



The errors in technique most likely to arise are those connected with 

 th(i picking up of the drop of blood by the cone. 



When the margin of the drop of blood on the end of the cone is ex- 

 amined under the microscope, it will be seen that it does not always come 

 absolutely up to the edge of the glass surface — a thin margin is sometimes 

 left. The blood Vjeing then a littli; further away, the .stream of oil will not 

 artect it in quite the same wa}'. Again, the drop is then not always (juite 

 circular in (jutline, and the flow of the corpuscles is liable thei-eby to be 

 slightly obstructed. 



With regai-d to the errors arising from want of deflniteness in the end- 

 point, it may be: ob.s(Mved that there an; three po.ssible stages whicli might 

 be adopted as indicating coagulation: — 



(1) The first appearance of a streak of clot. 



(2) The stop])age of the main flow of blood and the clear appearance of 



a laminated clot ; and 



(3) The comj)lete cessation of flow. 



On an avmage 00 seconds passes between (1) and (2), and 50 seconds 

 between (2) and (3). 



' In onlei' to oxjilaiii uliy tlu" blood does not loaguliHk' in the vessels, .some "have 

 as.sunied that tlie vascular endothelium secretes an anti-body (anticoagnlin). Loeb (:)) has 

 shown experimentally that this theory is not tenable. 



