or Bed Particles of the Mammiferous Animals. 107 



They have a very characteristic appearance, being remarkably 

 flat and pellucid, several generally touching at their edges so 

 as to form groups, scarcely ever turning over or even moving 

 in the fluid. It is obvious from the size, shape, and general 

 appearance of these particles, that they are not identical vv^ith 

 those which have been usually described as the nuclei of the 

 blood corpuscles. The average diameter of the disks in the 

 first instance was l-3429th of an inch. 



Besides the precaution concerning the preservation of the 

 blood, it is equally necessary to be careful as to how it is ob- 

 tained. The corpuscles are more or less modified very quickly 

 after extravasation ; and if some delay occur, and the drop 

 of blood, effiised into the subcutaneous tissue, require press- 

 ure to determine it to the surface, the corpuscles in that 

 blood may be expected to be irregular in form and mag- 

 nitude, many of them particularly presenting a granulated 

 appearance. Hence the glass should not be pressed upon the 

 wound, but merely lightly touched on a drop of the blood, 

 however small, that has appeared freely immediately after the 

 puncture. A specimen thus procured, and dried as before 

 noticed, will be excellent, although in all cases where it is 

 practicable a small incision directl}' into a superficial vein will 

 be preferable. 



The granulated particles are almost uniformly smaller than 

 the common disks, and it is not improbable that some of the 

 former may be produced by the irregular shrinking of the 

 latter. In some instances I could not detect any of the gra- 

 nulated corpuscles in the blood immediately after it was taken 

 from the animal, although they were to be seen abundantly 

 after a few hours' exposure in the serum to the atmosphere, 

 the temperature ranging between 45° and 50°. In one ob- 

 servation some of the extremely minute spherules, which are 

 not uncommon in the blood, were observed to attach them- 

 selves to a few of the smaller disks, so as to produce the gra- 

 nulated appearance. 



The blood corpuscles therefore are so singularly suscep- 

 tible of variation in size and form from the operation of very 

 slight agency, that there is probably no other microscopic 

 object of equal delicacy, or that requires so much experience 

 in its management. Hence it is not surprising that cursory 

 observers should have committed remarkable errors, and that 

 the history of the blood corpuscles, even after the labours uf 

 more careful inquirers, should have been so much obscured 

 by discrepancies, particularly when it is considered how the 

 inherent difficulties of the subject have been increased by the 

 imperfection of instruments. Hewson indeed, whose obser- 



