216 RED PARTICLES 



wise observed, that they had a dark spot (xcvi) in the middle, 

 which Father de la Torre took for a hole ; but upon a careful 

 examination I found it was not a perforation, and therefore 

 that they were not annular. I next made experiments by 

 mixing these particles with a variety of other fluids, and ex- 

 corpuscles of several mammalia/ I find that it is generally between one 

 third and one fourth of the diameter ; and the average thickness of the 

 human blood-corpuscle 1 estimate at j^i^^th of an English inch, and 

 the diameter at ^-g^th. These proportions are shown by the figures in 

 the * London and Edinburgh Philosophical Magazine' for Aug. and Sept. 

 1842, pp. 109, 170. More than a century ago, Jurin b estimated the 

 diameter of the blood-corpuscle of man at ^-^ ^th of an English inch ; 

 and Senac, c afterwards, at ^-gV^th and -jg-Vo^h of a French inch ; all, I 

 have no doubt, most accurate measurements of a great number, though 

 not of the majority, of the corpuscles in any drop of human blood. 

 According to Senac, d the English physicians regarded the corpuscles as 

 hollow on both sides ; which he disbelieved, concluding, I think, like 

 many of the old observers, only from what he saw in the lower vertebrate 

 animals. But in man and the mammalia generally, it is certain that 

 many of the corpuscles have, like a biconcave disc, a depression on each 

 side of the broad surface ; as inferred by Dr. Young, 6 and proved by 

 Dr. Hodgkin and Mr. Lister. f Some of them are without the depression, 

 and quite flat ; a few may even be slightly swoln on the broad surfaces, 

 and still more so at the edges, so that their relative thickness is variable. 

 This doubly convex form is very remarkable and general in the cor- 

 puscles of young embryos. Varieties in the form of the corpuscles are 

 mentioned in Notes cvi and ex ; the size and form of the corpuscles in 

 different animals, in Notes xcvm and cxvu ; and the central spot of 

 the corpuscles, of mammals, in Note xcvi. 



(xcvi.) The central spot of the blood-corpuscle of mammalia should 

 not be confounded with the nucleus of the blood-corpuscle of oviparous 

 vertebrata, described in Note en. The central spot is not visible in 

 the best focus and light ; then, if the object-glass of the microscope be 

 so slightly removed from the corpuscles as not to destroy the distinctness 

 of then* contour, a dark spot will appear in their centre ; if the glass be 

 next so far moved towards the corpuscles as to place them slightly 

 within the focus, the dark spot will become bright ; and when in a 

 clear light the spot is altogether invisible, it may be instantly brought 

 into view by diminishing the light, without altering the focus. Senac g 

 described the centre of the frog's blood-corpuscle as sometimes white 

 and sometimes black ; and Delia Torre h depicted a like variation in the 

 centre of the corpuscles of mammalia, though he mistook it for a hole. 



a See the Tables at the end of this e Med. Liter, p. 546, 8vo, Lond. 1813. 



chapter, Note cxvm*. f Phil. Magazine, 1827, vol. 2, p. 132. 



b Phil. Trans. 1718, vol. xxx, p. 762. s Traite du Cceur, ed. 1749, torn, ii, pp. 

 c Traite du Cosur, torn, ii, p. 655, ed. 656-7 ; and 2d ed. torn, ii, p. 277. 



1749; and 2d ed. torn, ii, p. 276. h NouveOsservazioneMicroscopiche,tab. 

 d Op. cit. torn, ii, p. 80, ed. 1749. xiv, figs. 3, 4, 4to, Napoli, 1776. 



