11G Remarks on the Globules of Blood and Pus. [Aug. 



rect idea of their structure. , The eye is best prepared for the 

 investigation, by beginning with the blood of a skate, of which 

 the panicles are so conspicuous, and of so unequivocal a form, 

 as to set aside at once the idea of a simple homogeneous sub- 

 stance. They are oval and depressed, like an almond, but less 

 pointed, and a little flatter; each of them contains a round nu- 

 cleus, which is wholly independent in its appearance of the 

 figure of the whole disc, being sometimes a little irregular in its 

 form ; seldom deviating from its central situation, but often 

 remaining distinctly visible while the oval part is scarcely per- 

 ceptible ; and as the portion of blood dries away, becoming 

 evidently prominent above the thinner portion. This nucleus is 

 about the size of a whole particle of the human blood, the whole 

 oval being about twice as wide, and not quite three times as 

 long; the nucleus is very transparent, and forms a distinct 

 image of any large object which intercepts a part of the light 

 by which it is seen, but exhibits no inequalities of light and 

 shade, that could lead to any mistake respecting its form. But 

 if we place some particles of human blood under similar circum- 

 stances, near the confine of light and shade, although they are 

 little, if at all, less transparent, we immediately see an annular 

 shade on the disc, which is most marked on the side of the centre 

 on which the marginal part appears the brightest, and conse- 

 quently indicates a depression in the centre, which Delatorre 

 mistook for a perforation. It is most observable when the drop 

 is drying away, so that the particles rest on the glass: and when 

 a smaller particle is viewed, it has merely a dark central spot, 

 without any lighter central space. Nor have the particles ever 

 appeared to me " as flat as a guinea," although their axis is 

 sometimes not more than one-third or one-fourth of their greatest 

 diameter; if they were much thinner than this, their diameter 

 would be more diminished than it is when they become sphe- 

 rical, by the effect of an aqueous fluid : while this form cor- 

 responds to a diminution to about f of the original diameter. 

 They may indeed possibly absorb a part of the surrounding 

 moisture in the change: but they do not seem to have their 

 dimensions much affected by the fluid in which they are sus- 

 pended, since they may easily be spread thin on glass, and dried, 

 without much change of their magnitude, at least in the direc- 

 tion of the surface to which they adhere: and they remain dis- 

 tinct as long as the access of moist air is completely excluded. 

 When they have been kept for some time in water, and a little 

 solution of salt is added, their form and structure, as Mr. 

 Hewson has observed, are more easily examined, and appear to 

 resemble those of a soft substance with a denser nucleus, not 

 altogether unlike the crystalline lens together with the vitreous 

 humour, as seen from behind : but with respect to a central 



