194 JOHN TAIT. 



Palinurus, however, whose blood forms such a stiff coagulum, the 

 power of autotoiny is present in very marked degree. Thus the form 

 of coagulation associated with the presence of explosive cells does not 

 imply absence or defective power of autotomy. 



If, again, we direct our attention to the Crustacea that possess in- 

 coagulable, or rather non-coagulating, blood-plasma (type A), we find 

 the evidence equally contradictory. Thus in Maia and in Cancer, 

 both of them forms with non-coagulating plasma, power of autotomy 

 is marked. In the spider-crab, Inachus doi^nchus, whose type of blood 

 coagulation likewise falls under group A, the presence of autotomy 

 is unusually difficult to demonstrate. It seems that no constant 

 relationship exists between power of autotomy and any special form of 

 blood coagulation. 



The assumption witli which we originally started, viz, that the 

 property of coagulability in blood plasma exists or has been evolved 

 for the sole purpose of arresting hjemorrhage, may however be un- 

 warranted. All the microscopical observations made on the arrest of 

 haemorrhage from a vessel, whether in invertebrates or in vertebrates, 

 including mammals, go to show that the opening is plugged chiefly by 

 adhesion and agglutination of cells at the cut surface. The blood of a 

 hfemophilic person forms a perfectly firm clot : in spite of the presence 

 of the clot, however, blood continues to ooze for hours and even days 

 from a wound. Again, we meet with coagulability in physiological 

 fluids other than blood. Milk clots in the stomach : yet no one has 

 suggested that this coagulation has a merely mechanical function. 

 Considerations such as these warn us against drawing premature con- 

 clusions in regard to the purpose for which coagulability exists in the 

 blood plasma. In circulating blood there are multitudinous chemical 

 processes constantly going on, the nature of which is entirely hidden 

 from us. Who can say that coagulability is not primarily concerned 

 in some of these hidden processes ? 



As a matter of fact, when we compare the actual time taken for 

 natural arrest of hajmorrhage from the terminal segment of one of the 

 limbs of Maia and of Palinurus respectively, we find that, while the 

 haemorrhage is, to begin with, equally profuse in both cases, the Maia 

 wound is closed as soon as the Palinurus wound. Maia blood is 

 characterized by the absence of all plasma coagulation. Palinurus 

 blood is highly coagulable. Until we have further knowledge as to 

 the raiso7i d'etre of coagulability in blood plasma, attempts to cor- 

 relate by a imori methods, different types of blood coagulation with 

 special physiological conditions can be but shots in the dark. 



I shall conclude this physiological discussion by referring shortly to 



