130 On the Value of High Puivers 



scribed the prism,* I seem to have incurred the charge of plagiarism. 

 The prism last employed of this form was made fourteen years ago, 

 as I found that it could be conveniently edged down, so as to be placed 

 deep in the setting, close behind the back lens of the object-glass. 



I have no wish to disparage or criticise forms of binocular 

 microscopes designed by others, as refracting prisms perform excel- 

 lently, and perhaps the only condition that has made the now 

 universal form so popular, is that it leaves the single body of the 

 microscope intact, not in any way requiring a difference in the con- 

 struction, or interfering with its ordinary use. 



Other known constructions are all more complicated, and as the one 

 principle appears to be the division or bisection of the object-glass 

 by using half for each eye, and if in the main tube the direct 

 image is straightway obtained, I do not see how definition can be 

 improved by any intervening contrivance. The only question is 

 whether the image in the inchned tube can be brought to the eye 

 by any more simple means than the present reflecting prism. 



V. — On the Value of High Powers in the Diagnosis of Blood 

 Stains. By Joseph G. Eichardson, M.D,, Lecturer on Pa- 

 thological Anatomy in the University of Pennsylvania, and 

 Microscopist to the Pennsylvania Hospital. 



{Bead be/ore the Biological and Microscopical Section of the American 

 Academy of Natural Sciences.) 



Plate LXXIII. (Upper portion). 



In the pages of the ' American Journal of the Medical Sciences ' 

 for July, 1869, appeared an article on the detection by the micro- 

 scope, of red and white corpuscles in blood stains, in which I advo- 

 cated the employment of high powers in such examination, and 

 asserted that by their aid I had been able to demonstrate that the 

 residuum of a dried blood-clot, left after the action of pure water, 

 so long mistaken by Virchow, Eobin, and their followers, for " pure 

 fibrin," was composed chiefly of the cell-icalls of the red blood- 

 corpuscles, and that by proper management these capsules of the 

 red disks could be brought clearly enough into view to enable me 

 to measure them accurately, and so distinguish the dried blood of 

 man from that of an ox, pig, or sheep, with a certainty disputed by 

 Caspar, Wyman, Fleming, and other previous observers. 



This possibility of recognizing blood-globules when dried en 

 masse, is of course closely associated with, if not actually dependent 

 upon, their possession of a cell-wall, as maintained in my paper on 

 tbe cellular structure of the red biood-corpuscle, in the ' Trans, of 

 the Am. Med. Asi^oc' for 1870 (the theory being mainly deduced 



♦ ' M. M. J.,' May, 1S73, \\ -^^- 



