STRUCTURE OF COLORED BLOOD-CORPUSCLES. 81 



sented by two straight and parallel lines, connected at their extremities by 

 two semicircular ones, and not showing merely their central concavity, as 

 usually represented. 



The question whether or not colored blood-corpuscles possess an investing 

 membrane has been much discussed, Hewson, who, as I have already stated, 

 showed that these corpuscles are not perforated, contended that the dark spot 

 in the middle, believed by Torre to be a perforation, " is a solid particle con- 

 tained in a flat vesicle, whose middle only it fills, and whose edges are hollow, 

 and either empty or filled with a subtile fluid."* He detailed the following 

 experiments : " Take a drop of the blood of an animal that has large particles, 

 as a frog, a fish, or, what is still better, of a toad ; put this blood on a thin 

 piece of glass, as used in the former experiment, and add to it some water 

 first one drop, then a second, and a third, and so on, gradually increasing the 

 quantity; and in proportion as water is added, the figure of the particle 

 will be changed from a flat to a spherical shape ; ... it will roll 

 down the glass stage smoothly, without those phases which it had when 

 turning over when it was flat ; and, as it now rolls in its spherical shape, the 

 solid middle particle can be distinctly seen to fall from side to side in the 

 hollow vesicle, like a pea in a bladder." He added: "From the greater 

 thickness of the vesicles in the human subject, and from their being less 

 transparent when made spherical by the addition of water, and likewise from 

 their being so much smaller than those of fish or frogs, it is more difficult to 

 get a sight of the middle particles rolling from side to side in the vesicle, 

 which has become round ; but with a strong light (these experiments were all 

 made with daylight, in clear weather) and a deep magnifier, I have distinctly 

 seen it in the human subject, as well as in the frog, toad, or skate." Another 

 experiment he describes thus : "If a saturated solution of any of the common 

 neutral salts be mixed with fresh blood, and the globules (as they have been 

 called, but which for the future I shall call flat vesicles) be then examined in 

 a microscope, the salt will then be found to have contracted or shriveled the 

 vesicles, so that they appear quite solid, the vesicular substance being closely 

 applied all around the central piece." Furthermore, "the fixed vegetable 

 alkali and the volatile alkali were tried in a pretty strong solution, and found 

 to corrugate the vesicles." 



The vesicular nature of colored blood-corpuscles, thus announced more 

 than sixty years before the publications of Schleiden and Schwann, so per- 

 fectly fits into their cell-schema that many suppose that they have originated 

 this view of the constitution of the corpuscles. But in point of fact they have 

 in this respect followed Hewson. According to Schwann, t the red blood- 

 corpuscle is a cell, and consists, like every other cell of the body, of a 

 membraneous envelope, a nucleus, and liquid contents; the credit of the 

 observation of the "rolling around" of the nucleus is given by Schwann to C. 



* " On the Figure ami Composition of the Bed Particles of the Blood, commonly called 

 the Bed Globules." Philosophical Transactions, vol. 63, Partn., p. 310 et seq. (read June 

 17 and 20, 1773). "A Description of the Bed Particles of the Blood in the Human 

 Subject and in other Animals, being the remaining part of the Observations and Experi- 

 ments of the late Win. Hewson." By Magnus Falconer. London, 1777, p. 221 et seq. 



t " Mikroskopische Untersuchungen iiber die Uebereiustimmung in Structur und Wachs- 

 thurn der thierischen und pfianzlichen Organismen." Berlin, 1839, pp. 74, 75. 



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