728 SPECIAL PHYSIOLOGY. 



in the liquor sanguinis a fibrino-genous substance, and that by the es- 

 cape of the former and its union with the latter, the act of solidification 

 is effected. But, since dead animal tissues of all kinds, and even clots, 

 or solidified fibrin itself, either fresh, or dried and powdered, produces 

 the same effect, it may be that the action of the corpuscles, in causing 

 coagulation of the fibrin, is not a vital process; and that if, as supposed, 

 their contained globulin escapes, by exosmosis, through their envelopes, 

 into the liquor sanguinis, this is, in reality, a post-mortem event. 



Finally, therefore, it is submitted that, out of the body, the solidifi- 

 cation of the fibrin, which is the sole cause of the coagulation of drawn 

 blood, is due to a mere physical, molecular, or molar change, resulting 

 in its transformation from a liquid to a pectous state, as is common to 

 colloidal bodies ; that this change is permitted, after the life of the 

 blood, or the incessant nutritive mutations which occur in living blood, 

 cease ; that it is accelerated, or induced, by the contact of dead mat- 

 ter, either proper or extraneous, to that fluid, and that it is to be re- 

 garded, not as a token of life* but as a sign of death. When coagula- 

 tion occurs within the body, it is still under conditions indicative of 

 the diminution or cessation of the ordinary vital interchanges of the 

 blood, and so may be equally regarded as a physical process, or, at 

 least, as one of those examples in which the essential cause is physical, 

 though sometimes it may be utilized, and directed to certain formative 

 ends. Lastly, if this view be maintained, the fibrinous fibrillae of clots 

 formed in the living bloodvessels, or extravasated amongst the tissues, 

 cannot be supposed themselves to be converted, any more than the red 

 corpuscles, into organized tissue elements ; but, by their trabecular 

 arrangement, they may facilitate the penetration into such clots, of an 

 organizable blastema, with nuclei or nucleated gymnoplastic cells, and 

 intercellular substance, for the production of newly formed tissue. 



The formation of an external clot at the mouth of a wounded or divided 

 vessel, is the first step taken by nature, in the effort to close the vessel ; to 

 this, succeeds the formation of an internal clot, the base of which, in a divided 

 vessel, corresponds with the wound, the apex extending towards the heart, as 

 far as the nearest branch of any size. From the divided edge of the vessel, a 

 nutritive plasma, or blastema, is poured out, in which nuclei and nucleated 

 cells, probably derived from the surrounding cell elements, appear, and form 

 the future areolar tissue, with its capillary network, which closes the aperture 

 in the vessel. In the case of a completely divided artery, the muscular coat 

 of the vessel contracts, and retracts within the sheath, and so helps its clos- 

 ure : a lacerated or twisted artery retracts even more securely than one cut 

 cleanly across. When an artery is tied, as in surgical operations, its middle 

 and internal coats are cut through by the thread, whilst the outer one is in- 

 closed in the knot ; the two former tunics contract, and turn in towards the 

 area of the vessel, and it is upon their cut edges that the primary clot first 

 forms, and from them, that the new tissue, which closes the vessel, is pro- 

 duced ; the constricted part of the outer coat sloughs, and permits the ligature 

 to come away. The artery is closed, and shrinks up to the nearest branch, 

 the primary clot being absorbed : the collateral vessels are greatly increased in 

 diameter, to carry on the circulation beyond the point of ligature. Pressure, 

 by aid of a needle passed through the soft parts upon the side of a divided ar- 

 tery of moderate size, enables its cut end to close : this is now sometimes em- 

 ployed after operations, and is known as acupressure. (Simpson and others. ) 



