1863.] 581 



best energies of many very able men, among whom may be men- 

 tioned, for example, such distinguished Fellows of this Society as 

 John Hunter and Hewson ; so that it might well seem presumptuous 

 in me to hope to communicate anything new regarding it, were it 

 not that the constant progress of Physiology and the allied sciences 

 is ever opening up fresh paths for inquiry, and ever affording fresh 

 facilities for pursuing them. Indeed, my difficulty, on the present 

 occasion, does not depend so much on the lack of materials as on 

 the complicated relations of the subject, which make me almost de- 

 spair of being able, in the short time that can be devoted to a lecture, 

 to give, in anything like an intelligible form, even an adequate selec- 

 tion of the facts at my disposal. 



It may, in the first place, be worth while, more especially for the 

 sake of any present who may not be physiologists, to mention 

 very briefly some well-known general facts respecting the con- 

 stitution of the blood. The blood, if examined by the microscope 

 within the vessels of a living animal, is seen to consist of a liquid 

 and numerous small particles suspended in it. The liquid is termed 

 the " liquor sanguinis," the particles the "blood-corpuscles." Of 

 these corpuscles a few are colourless, and are named the " colourless " 

 or " white corpuscles." The great majority are coloured and cause the 

 red appearance of the blood, and hence are called the "red cor- 

 puscles." Soon after blood has been shed from the body, it passes 

 from the fluid into the solid form. This depends upon the deve- 

 lopment in the blood of a solid material termed " fibrin," so called 

 from its fibrous nature, consisting, as examined by the naked eye, of 

 tenacious fibres, and having the same character also under the 

 microscope. These fibres form a complicated network among the 

 blood- corpuscles, and from their tenacity are the cause of the firm- 

 ness of the clot. Soon after the process of solidification or coagulation 

 is complete, the fibrin exhibits a disposition to shrink, and squeezes 

 out from among the corpuscles entangled in its meshes a straw- 

 coloured fluid termed the serum, very rich in albumen, in fact very 

 similar in chemical composition to the fibrin, which, in its turn, may 

 be said to be identical chemically with the material of muscular fibre. 



The question before us, therefore, is, What is the cause of the de- 

 velopment of this solid material, the fibrin? The subject may be 

 looked at in two aspects, first, as to the essential nature of the 



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