220 RED PARTICLES 



little with the red particles ; then with a soft hair pencil spread 

 a little of it on a piece of thin glass, and place this glass in the 

 microscope, in such a manner as not to be quite horizontal, 

 but higher at one end than the other, by which means the serum 

 will flow from the higher extremity to the lower ; and as it flows, 

 some of the particles will be found to swim on their flat sides, 

 and will appear to have a dark spot in their middle (see Note 

 xcvi) ; others will turn over from one side to the other, as they 

 roll down the glass. No person who sees them turn over can 

 doubt of their being flat ; he will see them, in turning, have 

 all the phases that a flat body has ; first, he will see them on 

 one side, then rise gradually on the edge, and turn over to the 

 other side. I have in this way shown their figure to a number 

 of curious persons, and particularly to many students of ana- 

 tomy, who have attended lectures in London within the last 

 six years. If instead of serum the particles should be diluted 

 with water, containing rather more salt than serum does, or if 

 instead of human blood that of an animal with larger particles 

 be used, then they will sometimes be seen not only flat, but a 

 little bended, like a crooked piece of money. 



These experiments not only prove that the particles of the 

 blood are flat, and not globular, but likewise, by proving that 

 they are flat, they show that they are not fluid, as they are 

 commonly believed to be (xcix) ; but, on the contrary, are 

 solid, because every fluid swimming in another which is in 

 larger quantity, if it be not soluble in that other fluid, becomes 

 globular. This is the case when a small quantity of oil is 

 mixed with a larger quantity of water, or if a small quantity 

 of water be mixed with a large one of oil, then the water ap- 

 pears globular ; and as these particles are not globular but flat, 

 they must be solid, a circumstance that will appear still more 

 evident from future experiments. 



It is necessary to remark, that in a few minutes after the 



(xcix.) Haller a says of them, "Solidi, perpetui, circumscripti, certa 

 magnitudine et figura, certa ferri portione prsegnantes, in fluido in- 

 visibili moventur." Senac, b too, considered the corpuscles as solid : 

 see Note cvm. 



a Elementa Physiologiae, torn, ii, p. 52. b Traite du Coeur, torn, ii, p. 665, ed, 1 749 ; 

 4to, Lausannse, 1760. and ed. 1774, t. ii, pp. 278, 283. 



