v THE BLOOD: PLASMA 135 



been too incomplete to make it the basis of a theory so opposed to 

 observations and experiments conducted on simpler and, therefore, 

 more convincing lines. Lymph contains neither erythrocytes nor 

 platelets, as shown by Fano, and yet it coagulates. 



(c) The third point in the theory of coagulation is to determine 

 on which or what chemical constituents of the blood the formation 

 of fibrin depends, since it is insoluble and cannot, therefore, pre- 

 exist as such in the blood. 



It was pointed out by Hewson (1770) and by G. Miiller (1832) 

 that the mother-substance of fibrin is derived, not from the 

 corpuscles, but from the constituents of the blood plasma. Hewson 

 was the first to obtain salted plasma comparatively free from 

 corpuscles, and noted that it formed a white clot on the simple 

 addition of water. Joh. Miiller succeeded in filtering frog's blood, 

 in which coagulation had been retarded with a sugar solution, 

 thus separating the corpuscles that remained on the filter from the 

 colourless plasma of the filtrate, and obtained in the latter a clot of 

 pure fibrin. The first, however, to demonstrate that coagulation 

 is a change of chemical state in a substance of the plasma which 

 he termed fibrinogen (which is found isolated in the transudates 

 already referred to, and mixed with serum globulin and serum 

 albumin in the plasma), was A. Schmidt. 



He assumed that two elements enter into the composition of 

 fibrin : fibrinogen (the fibrinogenic substance), and paraglolulin 

 (fibrinoplastic substance), explaining by' this the observations of 

 Buchanan, as cited above. Subsequently, however, it was shown 

 by Hammarsten (1875), and confirmed by others, that paraglobulin 

 takes no part in the formation of the clot, since the blood contains 

 an equal amount both before and after coagulation, and since a 

 solution of pure fibrinogen obtained from salt plasma can yield a 

 fibrinous clot 011 adding a little watery extract of serum, which is 

 quite free from paraglobulin. 



(d} A fourth problem : granted that fibrinogen is able to produce 

 fibrin by a change in its chemical state, it must be determined in 

 what this change consists. 



This question is attacked in the later work of Hammarsten, 

 Arthus, Lilienfeld, Car bone and others. 



Some hold the coagulation of blood to be a phenomenon analogous 

 to the curdling of milk. The substance derived from the corpuscles 

 which excites coagulation splits up the fibrinogen into two new 

 globulins thrombosin, which is insoluble, and changes into fibrin : 

 and fibrinoglobulin, which remains in solution in the plasma. 

 During this splitting of the fibrinogen, i.e. hydration, the chemical 

 association of water with the proteins occurs. A. Schmidt 

 has recently shown that pure horse's plasma, dried before coagula- 

 tion, weighs about 2 per cent less than an equal amount of the 

 same plasma dried after coagulation. 



