52 SCIENCE PROGRESS 



physiologists have recognised to be, next to the colour, its most 

 distinctive feature outside the body. A gradual change in 

 consistence takes place from the moment blood is shed, until, 

 as a firm jelly, it forms a clot which is a cast of the vessel 

 containing it. The plasma or fluid in which during life the 

 red corpuscles and leucocytes floated has thus formed a single 

 coherent mass of fibrin and corpuscles. This forthwith com- 

 mences to shrink, with the consequent production of a spon- 

 taneously non-coagulable liquid or blood-serum. 



In 1891 Lister 1 drew attention to the fact that, although 

 blood may clot, no marked retraction of the clot due to a 

 shrinking of the fibrin occurs when blood has been received 

 in a vessel rendered sterile by heat or by washing it out with 

 weak perchloride of mercury. A similar phenomenon is 

 frequently seen when blood is collected for obtaining antitoxic 

 sera. Hayem 2 and his pupils have also observed the absence 

 of serum from the clotted blood of patients with pernicious 

 anaemia or purpura haemorrhagica. They attach a special 

 importance to this non-retraction of the clot for the positive 

 diagnosis of pernicious anaemia and most forms of purpura 

 haemorrhagica, and consider the phenomenon is of even greater 

 value than a histological examination for the recognition of 

 the former disease. This non-retraction of the clot is at present 

 unexplained, but since it is a feature of clotted plasma in con- 

 trast to normal clotted blood, it is probably dependent in some 

 way upon influences exerted on the fibrin by the imprisoned 

 corpuscles or, according to Hayem, the blood-platelets, since 

 the plasma of birds, which may contain only a few or no 

 corpuscles, will, on being caused to clot by the addition of 

 tissue-extract, show no subsequent retraction of the clot — a fact 

 which has been noticed by Delezenne, 3 Fuld, 4 and Spangaro. 5 

 The fibrin, which forms but a very small amount of the bulk of 

 the clot, subsequently alters in its physical characters, becoming 

 more soluble. The extent of fibrinolysis and the rate at which 

 this occurs differs in different animals; it is also a subject of much 

 interest, since a study of the conditions under which it occurs 



' Lancet, p. 1082, 1891. 



2 La Semaine medicate, November 1896 ; Coniptes rend. January 1901. 



3 ArcJi. de Physiol, p. 333, 1897. 



4 Hofmeister's Beitrage, ii. p. 514, 1903. 



5 Arch. ital. de Biologie, xxxii. p. 210, 1900. 



