THE BLOOD. 547 



snails. The characteristic of these substances which prevent clotting is, 

 to repeat, that they evidently do not themselves directly affect the coagu- 

 lation process, but excite the organism to the formation of products which 

 tend to prevent the blood from forming a clot. 



Besides these substances which exert a secondary effect upon the 

 coagulation, we know of substances which directly prevent it. To these 

 substances belongs hirudin, which, by reason of the extensive studies of 

 Jakobj, has recently excited much interest. Hirudin is formed in the oral 

 glands of leeches. 1 It is quite stable towards heat and is soluble in water. 

 After injection into the organism it appears unchanged in the urine. It 

 is not yet perfectly clear how hirudin acts. It is apparently able to neu- 

 tralize a part of the fibrin ferment. 2 It is still an open question how we 

 can best picture this process. It is usually assumed that the active ferment 

 possesses groups which enable it to react with definite groups of other 

 compounds. These groups impart to the ferment its specific nature. If 

 now the ferment comes in contact with a substance which is capable of 

 engaging these groups, i.e., combining with them for example, the ferment 

 then becomes inactive. Substances like hirudin have been obtained from 

 other blood-sucking animals, e.g., from the wood-tick (Ixodes ricinus) and 

 from Anchylostomum caninum. 



It is an old observation that the blood of animals which have died from 

 snake-bite, often does not coagulate. 3 The poison from the cobra especially 

 has been carefully studied. It is supposed to contain a substance which 

 acts upon the kinase, i.e., the activator of the zymogen of the fibrin-ferment. 

 It is clear that if the function of this activator is disturbed, a coagulation 

 cannot take place. 



Besides the substances which prevent the coagulation of blood, we know 

 of others which accelerate it. In this respect we will recall the effect of 

 calcium salts. Their internal application is said to favor the formation of 

 blood-clot. Another substance which is used much more extensively 

 for this purpose is gelatin. 4 It is altogether impossible to state why this 

 property should be ascribed to gelatin, and if it really does exert the 

 desired effect it is still more difficult to explain it. At all events, the state- 

 ments concerning it that are to be found in the literature are very con- 

 tradictory. 



We have up to the present time intentionally disregarded a question of 



1 Haycraft: Arch, exper. Path. Pharm. 18, 209 (1884). Franz: ibid. 49, 342 (1901). 

 Andreas Bodong: ibid. 52, 242 (1904). 



2 Fuld and Spiro: Hofmeister's Beitr. 5, 171 (1904). P. Morawitz: Arch. klin. Med. 

 79, 432 (1904). 



3 Fontana : On Poisons. London, 1787. Morawitz: Arch. klin. med. 80, 340 

 (1905). 



4 Dastre and Floresco: Compt. rend. soc. biol. 48, 243 and 358; Arch, physiol. 28, 

 302. 



