THE FLUIDS OF THE BODY 73 



9 



drawn through a bloodvessel, from side to side, fibrin filaments 

 shoot out from the thread, as well as from the wound inflicted 

 on the vessel by the needle which was used to draw it 

 through. 



Plasma contains a substance which sets into fibrin. It has 

 been termed " fibrinogen." It is present in lymph, and in 

 almost all forms of exuded lymph. If sodium chloride (common 

 salt) is added to plasma until it is half saturated until it has 

 dissolved half as much as the maximum quantity which it 

 can dissolve fibrinogen is thrown down as a flocculent pre- 

 cipitate. It can be redissolved and reprecipitated until it 

 is pure. When fibrinogen was separated from plasma a step 

 was taken towards the explanation of coagulation. Under 

 certain conditions fibrinogen sets into fibrin. The question 

 which then presented itself for solution was as follows : What 

 is the substance which, by acting upon or combining with 

 fibrinogen, converts it into fibrin ? The clue to the solution of 

 this question was obtained from the consideration of certain 

 observations made by Andrew Buchanan in 1830, but long 

 neglected, because their significance was not understood. 

 Buchanan had observed that some specimens of lymph exuded 

 into a lymph-space the peritoneal cavity, for example will 

 clot ; others will not. He noticed that they clot when, owing 

 to puncture of a small bloodvessel during the process of drawing 

 them off, they are tinged with blood. Determined to ascertain 

 which of the constituents of blood is effective in rendering non- 

 coagulable effusions capable of clotting, he added to them in 

 turn red blood-corpuscles, serum, and the washings of blood- 

 clot. Either of the two latter was found to contain the clot- 

 provoking substance. Thirty years later a German physiolo- 

 gist prepared fibrinogen from effused lymph by precipitating it 

 with salt. He also treated serum in a similar way, precipitating 

 a protein which he termed fibrinoplastin. When these two sub- 

 stances were dissolved and the solutions mixed, he obtained a 

 clot, which he regarded as a compound of fibrinogen and fibrino- 

 plastin. Subsequently he found that the mixture did not 

 always clot, but he discovered that if he coagulated blood with 

 alcohol, and washed this residue, the washings added to the 

 mixed solution just referred to invariably produced a clot. 

 Thinking that the substance which he obtained from his 



