168 THE BLOOD. 



THEORIES OF COAGULATION. 



That the coagulation of the blood is due to the formation of an 

 insoluble substance (fibrin) in the plasma, was proved by Hewson, 1 who 

 showed that a coagulable plasma can be obtained by skimming, after 

 allowing the corpuscles to subside, in blood the coagulation of which 

 is delayed in any way, as by cold, by neutral salts, or by its retention 

 within a living vein. The old theories which ascribed the coagulation to 

 the cooling of the blood, to its coming to rest, to the running together 

 of the corpuscles into rouleaux, were all effectually disproved by the 

 same careful observer. Hewson also showed that ribrinogen (" coagul- 

 able lymph ") is precipitable and removable from plasma by a tempera- 

 ture of a little over 50 C. 2 Many*of Hewson's observations upon 

 coagulation were forgotten, and the facts rediscovered by subsequent 

 observers, but their accuracy was such that until comparatively modern 

 times no addition of any permanent value to the knowledge of the 

 subject was made. The most important of such additions (which was 

 also overlooked for many years) 3 was the observation of Andrew 

 Buchanan, that a substance could be extracted by water and solutions of 

 salt from lymphatic glands, from blood clot (especially the buffy coat), 

 and from various tissues, which had the property of producing the 

 coagulation of serous fluids, not themselves spontaneously coagulable, 

 such as hydrocele and pericardial fluid ; such action being comparable 

 to that of a ferment. But it is only quite recently that the active sub- 

 stance extracted by Buchanan has been examined, and found to belong 

 to the class of bodies known as nucleo-proteids. 



Schmidt's theory. A theory of coagulation, which was long accepted, 

 was that of Alexander Schmidt. Schmidt noticed that fluids which 

 contained fibrinogen but were not spontaneously coagulable, such 

 as pericardial or hydrocele fluid, coagulated on the addition of serum. 

 He ascribed the fibrin formation which resulted to the action (fibrino- 

 plastic action) of the globulin in the serum upon the fibrinogen of the 

 pericardial fluid. Since, however, the same globulin is already present 

 in abundance in pericardial and hydrocele fluid, it became clear that 

 this explanation of the action of serum was insufficient. It was, how- 

 ever, shown by Schmidt that a substance is extracted by water from the 

 alcohol precipitate of blood or serum, which possesses the property of 

 causing coagulation in these fibrinogenous liquids, or of causing coagula- 

 tion in plasma, the coagulation of which has been prevented by the 

 addition of neutral salts. To this substance the name of fibrin ferment 

 was applied, on account of its action resembling in general that of the 

 unorganised ferments or enzymes. Thus it was found to have its 

 activity accelerated by warmth, and destroyed by a high tempera- 

 ture (65 C.), and also to be capable of producing the coagulation of a 

 relatively large amount of fibrinogen. It was still held by Schmidt that 

 the globulin of serum takes an important share in the formation of fibrin. 



Hammarsten's earlier researches. Hamniarsten showed that serum 



1 Op. dt. 



2 For the history of this see Schiifer, Journ. PhysioL, Cambridge and London, 1880, 

 vol. iii. p. 185. 



3 Cf. Gamgee, "PhysioL Chemistry," 1880, vol. i., where will also be found an excellent 

 account of the earlier history of the subject of blood coagulation. See also Arthus, " Coag. 

 des liquides organiques," Paris, 1894, for a good epitome of the history of the subject up 

 to that date. 



