BODY FLUIDS AND CIRCULATION 127 



shed blood of Homarus and Ligia. In the first stage blood cells known as 

 explosive corpuscles stick to foreign surfaces and quickly disintegrate, 

 giving rise to localized clots; in the second, related to disintegration of 

 blood thigmocytes, gelation spreads to involve the whole plasma. The two 

 stages are fundamentally similar. 



Mean coagulum weights for decapods range from 3-6 g/1. plasma in 

 Gecarcinus to 16*6 g/1. in Panulirus. The coagulum includes cellular ele- 

 ments which are responsible for around a third to a fifth of the total. 

 Much individual variation is encountered in fibrinogen levels of various 

 species, and there is some evidence that fibrinogen concentration is mini- 

 mal at time of moult (Carcinus, Callinectes). Coagulation in shed blood 

 usually takes place within a minute, although many minutes often elapse 

 before flow is stopped at a wound. The heaviest fibrin-clots are formed by 

 macrurans (lobsters, crayfish). These are nearly equalled by the coagulum 

 of Dardannus (anomuran). Values for brachyurans are about a quarter of 

 those for Panulirus. Attempts have been made to correlate clotting ability 

 with other defensive properties, and in general it appears that blood 

 clotting is best developed in species lacking very hard external coverings 

 and showing low incidence of autotomy (91). 



Clotting in the blood of the lobster Homarus vulgaris and allied forms 

 is essentially different from the process in vertebrates. The haemolymph 

 contains a dissolved fibrinogen, which is converted into fibrin in shed 

 blood through the action of a thrombin-like catalyst termed coagulin. 

 The latter occurs in blood leucocytes (explosive cells, thigmocytes), in 

 muscle and other tissues. Coagulation begins with the disintegration of 

 blood leucocytes, which release coagulin. In the presence of Ca ++ ions 

 this factor accelerates the conversion of fibrinogen to fibrin, which forms a 

 homogeneous clot (49, 83). 



Some properties of lobster fibrinogen (Homarus) are as follows. The 

 concentration in the haemolymph is around 0-4%, but decreases greatly 

 in animals kept in captivity, apparently as the result of inanition. Clotting 

 is ineffective at concentrations below 0-15%. Fibrinogen can be salted out 

 of blood by the addition of half-saturated ammonium sulphate or sodium 

 chloride. Its isoelectric point lies at pH 4-1, and it shows optimal activity 

 (as measured by clotting time) at pH 7-2. Fibrin clotting is prevented by the 

 addition of citrate or oxalate, but not by hirudin or heparin except in high 

 concentrations. 



Various methods have been described for the separation of lobster 

 fibrinogen, including electrophoresis. The following are procedures which 

 have been used for obtaining noncoagulated crustacean (lobster) plasma. 

 Collect blood in a paraffin tube containing 1 ml of 0-2 M Na citrate per 

 10 c.c. of blood or 1 mg K oxalate per ml of blood. Centrifuge the fluid to 

 remove the cell coagulum. Clotting is produced in this citrated or oxalated 

 plasma by the addition of CaCl 2 and muscle extract. The coagulation factor 

 is not specific among crustaceans, and is not interchangeable with verte- 

 brate thromboplastic factor and thrombin (35, 49). 



