OF THE BLOOD. 215 



scopical observers have agreed in their being spherical (xcin). 

 When we consider how many ingenious persons have been 

 employed in examining the blood with the best microscopes, it 

 will appear wonderful that the figure of these particles should 

 have been mistaken ; but our wonder will be lessened when we 

 consider how many obvious things are overlooked, till our at- 

 tention is very particularly directed to them ; and, besides, the 

 blood in the human subject and in quadrupeds is so full of 

 these particles, that it is with great difficulty we can see them 

 separate, unless we find out a method of diluting the blood. 

 It is to such a discovery that I attribute my success in this 

 inquiry; for having examined the blood as it flows from the 

 vessels of the human body, it appeared a confused mass, not- 

 withstanding I spread it thin on a glass, or a piece of talc. 

 It then occurred to me to dilute it, but not with water, for 

 this I knew dissolved the particles, but with serum, in which 

 they remained undissolved (xciv). By the serum I could dilute 

 it to any degree, and therefore could view the particles distinct 

 from each other ; and in these experiments I found that these 

 particles of the blood were as flat as a guinea (xcv). I like- 



(xcin.) See Note xc. 



(xciv.) Muys a mentions the difference between the effect of serum 

 and water on the corpuscles. That they are not dissolved by water was 

 observed by Dr. Young. 5 It merely deprives them of their colouring 

 matter, leaving undissolved the pale membranous base of the disc, and 

 the nucleus also, when there is one ; see Note en, pp. 222-3 : and for 

 an account of the action of water, and fluids of different densities, on 

 the blood-corpuscles, with a description of their power of endosmose and 

 exosmose, see the observations by Dr. Rees and Mr. Lane. c The cor- 

 puscles should be examined in their own serum ; for it may be difficult 

 to distinguish their outline in the serum of another animal, which is 

 apt to cause them to aggregate into clumps. The serum of the horse 

 has this effect remarkably on the corpuscles of many mammalia ; the 

 addition of a small quantity of salt to the serum will diminish or destroy 

 the clumping of the corpuscles : see Notes xxiu and cxi. 



(xcv.) They are not nearly so thin, in relation to their breadth, as 

 a guinea, the thickness of which is about a nineteenth of its diameter. 

 Dr. Hodgkin and Mr. Lister/ indeed, state the thickness of the blood- 

 corpuscle to its diameter as 1 to 45 ; but this must be a misprint. 

 From measurements of the thickness, at the circumference, of the 



a Musculorum Artificiosa Fabrica. 4to, c Guy's Hospital Reports, 1841, vol. vi; 



Lud. Batav. 1751, p. 100. and 1843, vol. i. 



b Medical Literature, 8vo, Lond. 1813, d Philosophical Magazine, or Annals, &c. 



p. 547. vol. ii, 1827, p. 133. 



