726 SPECIAL PHYSIOLOGY. 



small, compact, and pale. In both kinds of vessels the broadest or 

 attached part, or base of the clot, is directed towards the heart. No 

 escape of ammonia can take place when a clot forms in a ligatured 

 artery, nor in that coagulation of the blood during life, which occurs 

 from the sudden destruction, in animals, of the substance of the ner- 

 vous centres. Nor can this explain the coagulation produced by the 

 injection of dead brain-substance, or of pus, into the blood, nor the 

 fact that blood inclosed between two ligatures in a dead vein speedily 

 coagulates; whilst blood similarly inclosed in a living vein remains 

 fluid, the facility for the escape of ammonia being apparently, in either 

 case, the same (Astley Cooper, Briicke, Lister). 



Indeed, this last-mentioned experiment, added to the well-known 

 circumstances, that blood, extravasated amidst the living healthy tissues, 

 remains for a long time fluid, whilst if in contact with inflamed vessels 

 or tissues deficient in vitality, or with the lining membrane of vessels 

 containing morbid deposits, or with dead animal substances out of the 

 body, it quickly coagulates, indicates a striking contrast between the 

 effect of contact of living and dead animal tissues on the blood, the 

 former, in some way, retarding or antagonizing the coagulation of that 

 fluid, the latter, in some way, accelerating or determining it (Lister). 



[At a recent meeting of the British Association for the Advance- 

 ment of Science, Dr. Richardson publicly withdrew his theory of co- 

 agulation of the blood, stating that further research had shown him 

 there were such strong physical objections to it as a theory, that it 

 was no longer tenable. Dr. Richardson also illustrated his present 

 views on the subject of coagulation, with special relation to the causes 

 of the phenomenon. Some recent experiments of his own on the in- 

 fluence of extremes of heat and cold on albuminous and fibrinous 

 fluids, have shown him that the process of coagulation in these fluids 

 is due to a communication of caloric force to them, and to a physical 

 or molecular change, determined by the condition of their constituent 

 water. Thus all substances which possess the power of holding blood 

 in the fluid condition, such as fixed alkalies, various soluble salts, and 

 volatile alkali, in every respect act after the manner of cold, render- 

 ing latent so much heat, in the absence of which the fibrin remains 

 fluid. In the opposite sense, every substance which combines with 

 water, and produces condensation, with liberation, quickens coagula- 

 tion. In other words, according to Dr. Richardson's present views, 

 coagulation is facilitated by heat and retarded by cold. 



He also stated that in the ordinary condition there is a constant 

 process, similar to coagulation, going on in the living body, in the 

 formation or construction of muscle, and a steady and persistent inter- 

 change of force from those parts which are solidified by cold arid fluid- 

 ified by heat, to those which are rendered solid by heat. He con- 

 cluded by stating that the process of rigor mortis was an illustration 

 of the same order of phenomena. (Am. Jour. Med. Sci., Jan., 1868, 

 p. 245.) F. G. S.] 



It has been suggested that the immediate cause of the coagulation 



