266 DISTURBANCES OF CIRCULATION 



to remain stagnant for a long period without clotting, depends 

 upon the same fact, namely, that normal endothelium neither 

 liberates coagulin itself nor injures the leucocytes so that they 

 disintegrate. Loeb recalls the observation of Overton that 

 lipoids are important constituents of the cell membranes, and 

 suggests a similarity between the vessel lining and the oiled 

 cannula. The suggestion that the vessel walls contain an anti- 

 coagulin could not be confirmed by Loeb. Since leucocytes are 

 constantly undergoing disintegration in the blood and tissues 

 under normal conditions, it might be asked why they do not 

 cause clotting then and there. In explanation Loeb advances 

 his observation that the coagulins are destroyed during cell 

 autolysis, and suggests that when leucocytes normally disintegrate, 

 the coagulins are first destroyed by autolysis. It has also been 

 shown that the cells and serum contain substances which inhibit 

 or prevent coagulation, and it is possible that these play an 

 important part under normal conditions in preventing coagu- 

 lation by products of cell disintegration, much as other anti- 

 enzymes are supposed to act in preventing autodigestion of 

 living cells. 



Coagulation of drawn blood may be retarded experimentally 

 by removal of the calcium by precipitation as oxalate, fluoride, 

 etc. ; also by diminishing the oxygen and increasing the CO 2 , 

 by addition of solutions of neutral salts in large amounts, by 

 diluting greatly with water, or by keeping the blood cold. 

 Coagulation may be hastened by moderate heat, by whipping, 

 exposure to air, by contact with much foreign matter, and by 

 the addition of watery extracts from many different tissues and 

 organs. 1 Of particular interest pathologically is the retardation 

 of coagulation that follows injections of proteoses (the so-called 

 " peptone " solution) and also by various other proteid-con- 

 taining solutions, such as organ extracts, bacterial toxins, snake 

 venoms, eel serum, extract of leeches or of Uncinaria, impure 

 nucleoproteid solutions, or solutions of various colloids. Most 

 of these substances (e. g., peptone, eel serum) cause reduction 

 of coagulability when injected into animals, and are without 

 effect on blood removed from the body. A few, however, 

 prevent coagulation of drawn blood (snake venom, extract of 

 leeches). When substances of the first class are injected in 

 sufficient quantities, there occurs first a period of accelerated 

 coagulation which may, particularly in the case of organ extracts, 

 cause prompt death from intravascular clotting ; if the animal 

 survives, there follows a period of decrease or total inhibition 

 l See Conradi, Hofmeister's Beitr,, 1901 (1), 136. 



