DR DAVY'S OBSERVATIONS ON BLOOD AND MILK. 55 



torn ; and, in the instance of serum, if not agitated, remains as a connected mass. 

 If now a glass rod be put into it, and witlidrawn through the supernatant serum, 

 it will come out not sensibly coloured by the red particles ; the surface of the 

 cruor round the rod will be seen to be raised a little in the act from adhering to 

 it, and then to return to its former level, shewing that the corpuscles adhered to 

 each other in the mass more strongly than to the glass : and, if the serum through 

 which the rod has been dra^vn is examined with the microscope, a small number 

 only of blood corpuscles will be detected in it. 



If, instead of allowing the cruor to remain undisturbed, it be broken up by 

 agitation with the serum, it will be found to be divided into clusters of corpuscles 

 and detached particles. When one of these clusters is placed under the micro- 

 scope, between two plates of glass, the adhering corpuscles forming the group are 

 seen to be attached, not by their broad or concave surfaces, as in the instance of 

 aggregation by piles, but by then- narrow rims. Now, if graduated pressure be 

 employed, so as to break up the cluster, just before separating, the adhering cor- 

 puscles will be seen to be elongated, as if drawn out almost to a fibre, and yet 

 when detached, the adhesion being overcome, recovering, and that suddenly, their 

 circular form : and, on relaxing the pressure, many of them will be seen to reunite, 

 sticking to each other even when in motion. 



This adhesive quality of the blood corpuscles is exei'cised, not only on each 

 other, but also on other substances, though, perhaps, in a less degree. Proof of 

 this is afforded when cruor has been allowed to remain, even but a short time, 

 in a glass tube, or any other vessel. The portion in contact with the bottom of 

 the tube is found to adhere to it, and is not easily detached ; whilst any that may 

 adhere to the sides commonly appears in streaks, the blood corpuscles being at- 

 tached to each other, and so producing a linear arrangement. 



This viscid property of the blood corpuscles must, I apprehend, be considered 

 as specially belonging to them, quite distinct from the fibrin, which appears to 

 be viscid only in its transition state, in the act of coagulating, — previously even 

 more liquid than serum attenuating the blood, and subsequently, as soon as co- 

 agulated, constituting the firmest and the cementing part of the crassamentiun. 

 The blood corpuscles, as regards this quality of viscidity, are far more constant ; 

 it belongs to them when fresh, probably when circulating in the vessels, — it is 

 exhibited in them long after removal from the living body, and is not even lost 

 with incipient putrefaction, and, connected with that, the change of the particles 

 to a globular form. 



