320 Addis 



On the other hand there is some reason to believe that the appearance 

 of such a thread does not necessarilj'- imply coagulation at all, but maj'^ be 

 a purely physical phenomenon. Mann, in his " Chemistry of the Proteids," 

 1906, p. 382, says: "Ramsden, in a paper not yet published, states that 

 fibrinogen solutions, free from fibrin ferment, can l)e made to yield mechani- 

 cal surface aggi-egates " indistinguishable from typical fibrin, and that 

 " fibrinogen, mechanically produced fibrin, and ferment-produced fibrin have 

 the same heat-coagulation temperature, 53°-58°." 



There is, therefore, the possibility that this may be an instance of the 

 mechanical production of fibrin. 



In the four methods which adopt the fibrin thread as their end -point 

 the method of demonstration is by the slow withdrawal of glass from blood, 

 just the circumstances under which Buck master has found this very early 

 appearance of fibrin to occur. 



To adopt this as the end-point would appear, therefore, to be very 

 fallacious, and to a certain extent it no doubt is so. In practice, however, 

 there is very often an appearance not of a thread but of a considerable 

 mass of fibrin, and there is no good reason to suppose that this is due to 

 anything but fibrin-ferment coagulation. 



Nevertheless, even when a fibrin thread is taken to indicate the 

 occurrence of coagulation, it is probable that it will not be very constant 

 in the time of its appearance, for fibrin is primarily deposited in an amorph- 

 ous and invisible condition, and it is only under the influence of mechanical 

 stress that it acquires the appearance of threads or of a visible mass. These 

 physical factors are impossible to control or keep constant. Possibly also 

 there may be conditions of the blood which favour or retard the appearance 

 of fibrin in a recognisable form. 



In the case of the indirect method of determining coagulation, various 

 alterations in the behaviour of the blood to its surroundings have been 

 adopted as end-points. All these are based on one change in the physical 

 character of the blood, i.e. a loss of fluidity. 



When clear signs of this are seen, it is assumed that coagulation has 

 occurred. This, however, is not always the case, for it is sometimes due 

 simply to agglutination of the corpuscles. 



As has already been mentioned, the agglutinability of the blood is 

 increased in disease, and for this reason methods which depend on an in- 

 direct method of determining coagulation will probably give untrustworthy 

 results in pathological conditions. 



Agglutination commences whenever the blood is drawn, and the longer 

 it is left exposed to air the more marked does it become. This is well seen 

 in using Brodie and Russell's method. If the blood after its introduction 

 into the apparatus is not put in motion for a minute or two, agglutination 

 may be so strong as to give all the signs which are considered to be conclusive 

 of coagulation ; although, if movement of the corpuscles had been induced at 

 once and repeated at short intervals, a coagulation time of 7 to 12 miniites 



