248 THE BLOOD. 



tion. But if to this solution is added a water-washed fibrin-clot or a 

 little blood-serum, it immediately coagulates, and may yield perfectly 

 typical fibrin. The transformation of the fibrinogen into fibrin requires 

 the presence of another body contained in the blood-clot and in the serum. 

 This body, whose importance in the coagulation of fibrin was first observed 

 by BucHANAN, 1 was later rediscovered by ALEXANDER SCHMIDT^ and 

 designated as fibrin ferment or thrombin. The nature of this enzymotic 

 body has not been ascertained with certainty. Although many investiga- 

 tors, especially English, consider fibrin ferment as a globulin, still more 

 recent experiments of PEKELHARING and others show that it is a nucleo- 

 protein which, according to HuiSKAMp ; 3 occurs in the thymus gland 

 partly as nucleohistone and partly in another form. Fibrin ferment 

 is produced, according to PEKELHARING, by the influence of soluble 

 calcium salts on a preformed zymogen existing in the non-coagulated 

 plasma. SCHMIDT admits the presence of such a mother-substance of 

 the fibrin ferment in the blood, and calls it prothrombin. The conversion 

 of this mother-substance into thrombin is a very complicated process, 

 which will be discussed under the coagulation of the blood. Thrombin 

 is like other enzymes in that the very smallest amount of it produces an 

 action, and its solution becomes inactive on heating. The velocity of 

 coagulation is dependent upon the quantity of thrombin, and FULI> 

 has found that at least within certain limits an increase of double the 

 quantity of enzyme causes an increase in speed of coagulation of one and 

 one-half. This closely corresponds to SCHULTZ'S law; but it is true only 

 for experiments with bird plasma and tissue extracts. MARTIN 4 has 

 found another law from experiments with plasma and snake-poisons 

 containing thrombin. According to him the behavior is as follows: 

 As in the casein coagulation with rennin, the celerity of coagulation 

 is inversely proportional to the quantity of ferment; and LOEB has 

 observed a similar conduct with invertebrates. The optimum of the 

 thrombin action lies at about 40 C. ; at 70-75 C. the enzyme is destroyed 

 in neutral solution. The question as to whether the thrombin found 

 in different animals is the same substance or whether we have several 

 thrombins, has not been decided. The latter is not improbable; neverthe- 



1 London Med. Gazette, 1845, 617. Cit. by Gamgee, Journal of Physiol., 1879. 



2 Pfluger's Arch., 6; see also Zur Blutlehre, 1892, and Weitere Beitrage zur Blut- 

 lehre, 1895. 



3 Pekelharing, Verhandl. d. Kon. Akad. d. Wetensch. te Amsterdam, 1892, Deel 1; 

 ibid., 1895, and Centralbl. f. Physiol., 9; Wright, Proc. Roy. Irish Acad. (3), 2; The 

 Lancet, 1892, and On Wooldridge's Method, etc., British Med. Journal, 1891; Lilien- 

 feld, Hamatol. Untersuch. Arch. f. (Anat. u.) Physiol., 1892; Ueber Leukocyten und 

 Blutgerinnung, ibid.; Halliburton and Brodie, Journal of Physiol., 17 and 18; Huis- 

 kamp, Zeitschr. f. physiol. Chem., 32; Pekelharing and Huiskamp, ibid., 39. 



4 Martin, Journ. of Physiol., 32; Hofmeister's Beitrage, 2; Loeb, ibid., 9. 



