THE CLOTTING OF THE BLOOD. 33 



down very much like plasmine. If after the removal of the first precipitate 

 more sodium chloride, and especially if magnesium sulphate be added, a 

 second precipitate is thrown down, less viscid and more granular than the 

 first. 



The second precipitate when examined is found to be identical with the 

 paraglobulin, coagulating at 75 C., which we have already seen to be a 

 constituent of serum. 



The first precipitate is also a proteid belonging to the globulin group, 

 but differs from paraglobulin, not only in being more readily precipitated 

 by sodium chloride, and in being when precipitated more viscid, but also in 

 other respects, and especially in being coagulated at a far lower temperature 

 than paraglobulin, viz., at 56 C. Now, while isolated paraglobulin cannot 

 by any means known to us be converted into fibrin, and as its presence in 

 the so-called plasmine does not seem to be essential to the formation of 

 fibrin out of plasmine, the presence in plasmine of the body coagulating at 

 56 C. does seem essential to the conversion of plasmine into fibrin, and we 

 have reason for thinking that it is itself converted, in part at least, into 

 fibrin. Hence it has received the name of fibrinogen. 



20. The reasons for this view are as follows : 



Besides blood, which clots naturally when shed, there are certain fluids 

 in the body which do not clot naturally, either in the body or when shed, 

 but which by certain artificial means may be made to clot, and in clotting 

 to yield quite normal fibrin. 



Thus the so-called serous fluid taken some hours after death 1 from the 

 pericardial, pleural, or peritoneal cavities, the fluid found in the enlarged 

 serous sac of the testis, known as hydrocele fluid, and other similar fluids, 

 will in the majority of cases, when obtained free from blood or other admix- 

 tures, remain fluid almost indefinitely, showing no disposition whatever to 

 clot. 2 Yet, in most cases at all events, these fluids, when a little blood, or a 

 piece of blood clot, or a little serum is added to them, will clot rapidly and 

 firmly, 3 giving rise to an unmistakable clot of normal fibrin, differing only 

 from the clot of blood in that, when serum is used, it is colorless, being free 

 from red corpuscles. 



Now blood (or blood clot, or serum) contains many things, to any one of 

 which the clotting power thus seen might be attributed. But it is found 

 that in many cases clotting may be induced in the fluids of which we are 

 speaking by the mere addition, and that even in exceedingly small quantity, 

 of a substance which can be extracted from blood, or from serum, or from 

 blood clot, or even from washed fibrin, or indeed from other sources, a sub- 

 stance whose exact nature is uncertain, it being doubtful whether it is a 

 proteid at all, and whose action is peculiar. 



If serum, or whipped blood or a broken-up clot be mixed with a large 

 quantity of alcohol and allowed to stand some days, the proteids present are 

 in time so changed by the alcohol as to become insoluble in water. Hence 

 if the copious precipitate caused by the alcohol, after longstanding, be sepa- 

 rated by filtration from the alcohol, dried at a low temperature, not exceed- 

 ing 40 C., and extracted with distilled water, the aqueous extract contains 

 very little proteid matter, indeed very little organic matter at all. Never- 

 theless, even a small quantity of this aqueous extract added alone to certain 

 specimens of hydrocele fluid or other of the fluids spoken of above, will bring 

 about a speedy clotting. The same aqueous extract has also a remarkable 



1 If it be removed immediately after death it generally clots readily and firmly, giving 

 a colorless clot consisting of fibrin and white corpuscles. 



2 In some specimens, however, a spontaneous coagulation, generally slight, but in ex- 

 ceptional cases massive, may be observed. 



3 In a few cases no coagulation can thus be induced. 



3 



