Dr. Buchanan on the Fibrin conicdned in the Animal Fluids. 139 



the process of coagulation. If this be true, it follows as a consequence, 

 that the two parts into which the blood separates spontaneously after 

 being drawn, are not the same as those of which the blood is seen to 

 consist, by the microscope, when it is circulating in the blood-vessels : 

 for the fibrin, which, in the latter circumstances is united to the solid 

 portion, is, in the former circumstances, dissolved in the liquid portion. 

 It appears to me that the whole of this doctrine is erroneous. I believe 

 the solid and liquid portions, of which the circulating blood is seen to 

 consist, under the microscope, to be the very same as the solid and 

 liquid portions into which the blood, after being drawn, spontaneously 

 separates : that the whole coagulum, or part which affects the solid 

 form after being drawn, existed previously within the blood-vessels in 

 the solid form : that during the coagulation of the blood there is no 

 mysterious precipitation of a solid previously held in solution, but 

 that the process of coagulation consists simply here as in the cases 

 already mentioned, in the aggregation of granules and globules pre- 

 viously existing diffused through the serous liquid, but not cohering : 

 and that the only peculiarity in the coagulation of the blood consists 

 in this, that some of the solid corpuscles, by the aggregation of which 

 the coagulum is formed, are red, while others are transparent, and that 

 the latter possess a much higher cohesive power than the former. It 

 follows, if these opinions be correct, that the term " liquor sanguinis " 

 should be banished from physiology, as conveying a whole series of 

 erroneous ideas as to the constitution of the blood. 



3. Fibrin exists in the bloody not in solution, but in the form of 

 transparent granules and vesicles. — In what way can the transparent 

 fibrin which exists in coagulated blood, be shown to exist in the solid 

 form in liquid blood ? It may be thought by many that this is a very 

 simple matter to determine ; that we have only to put liquid blood 

 under the microscope, when we shall at once be able to distinguish the 

 red from the transparent corpuscles. But all who are in the habit of 

 examining with the microscope the corpuscles in the animal fluids, 

 know that it is only when they are congregated in masses that their 

 colour is perceptible, so that we can determine whether they are red 

 or transparent : but that, when single globules are observed, they are 

 only distinguishable from the surrounding transparent liquid, by their 

 refractive power, which gives to them all the same solar yellow colour, 

 varying in tint according to the intensity of the light under which 

 they are seen. Thus it is, that the transparent corpuscles of blister 

 liquid are in no way distinguishable from red blood corpuscles intro- 

 duced into it 



It is only by examining the portion of the blood yielding a colourless 

 coagulum, separate from that yielding the red coagulum, that the 

 question at issue can be decided. I have already mentioned the cir- 

 cumstances in which the^eparation of these two portions of the blood 

 takes place ; now in all of these cases, so far as has yet been observed, 



