66 ENZYMES OR SOLUBLE FERMENTS. 



zymogen (Hammarsten). It occurs also in the stomach of children 1 

 and of man 2 , and Roberts has described a similar enzyme in the 

 pancreas of the pig, ox and sheep 3 . Rennin is stated to occur in 

 traces in urine 4 . 



Fibrin-ferment. 



Buchanan's work (1831) on the clotting of blood, more particularly 

 his experiments with ' washed clot,' when examined in the light 

 of our present knowledge, shows clearly that he was in reality 

 dealing with that factor in the whole process which was inde- 

 pendently discovered by Alexander Schmidt and more specifically 

 described by him in 1872 under the name of 'fibrin-ferment 5 .' Its 

 existence had been foreshadowed in some experiments made by Briicke, 

 in which he showed that the fibrinoplastic action of precipitated 

 paraglobuliri was partly at least dependent upon the admixture of some 

 other substance which he regarded as the truly fibrinoplastic factor. 

 Thus he showed among other things that the more a serum is diluted 

 before the paraglobulin is precipitated from it by means of CO 2 the 

 less marked are its fibrinoplastic powers 6 . Further Mantegazza had in 

 1871 put forward the view, also held by Buchanan, that the white 

 corpuscles play some important part in the formation of fibrin, without 

 in any way characterising the substance which he suggested was 

 probably discharged from them as the determinant of the whole 

 process 7 . The time was thus ripe for Schmidt's discovery 8 . He 

 prepared the ferment by precipitating serum with 15 20 volumes of 

 strong alcohol; the precipitate was treated for at least 14 days with 

 the alcohol to insure complete (?) coagulation and insolubility of the 

 proteids, after which time it was removed by filtration, dried in vacuo 

 over sulphuric acid, pulverised and extracted with distilled water in 

 volume equal to twice that of the serum originally employed. The 

 ferment solution thus obtained is by no means pure and not very 

 active. More recently Hammarsten has obtained the ferment in 

 solution free from paraglobulin 9 . He saturates serum with magnesium 

 sulphate at 30 and filters off the precipitated paraglobulin at the same 



1 Zweifel, Centralb. f. d. med. Wiss. 1874, No. 59. Hammarsten, Ludwig's 

 Festgabe, Leipzig, 1875. 



2 Schumberg, Virchow's Arch. Bd. xcvu. (1884), S. 260. Boas, Centralb. f. d. 

 med. Wiss. 1887, No. 23. 



3 Proc. Roy. Soc. No. 29, 1879, p. 157. 



4 See Helwes, Pfluger's Arch. Bd. XLIII. (1888), S. 384. 



5 An account of Buchanan's experiments has been given by Gamgee. Physiol. 

 Chemistry, Vol. i. 1880, p. 43. See also Jl of Physiol. Vol. H. (1879), p. 145. 



6 Sitzb. d. Wien. AJcad. Bd. LV. (2 Abth), 1867, S. 891. 



7 See Abst. in Maly's Bericht. Bd. i. (1871), S. 110. 

 8 Pfltiger's Arch. Bd. vi. (1872), S. 457. 



9 Ibid. Bd. xvm. (1878), S. 89 ; xxx. (1883), S. 457. 



