42 



American Quarterly Microscopical Journal. 



portant function of the fully-developed red ones, namely, the 

 transportation of oxygen. 



Upon further examination of the literature of this subject, 

 I find in Wagner's Pathology (p. i86), Charlton Bastian cited 

 as authority for the statement published in the British Medical 

 Journaliox 1868, that "red globules as well as white leave the 

 vessels in venous stases, scorbutus, etc., by means of amoeboid 

 movements." Not having had access to the Journal I do not 

 know upon what observations he based his statement, nor 

 whether he had made investigations similar to my own. 



A NEW DEVICE 



FOR DARK-FIELD 

 TION. 



ILLUMINA- 



BY PROFESSOR WM. LIGHTON. 



I HAVE been quite interested, 

 lately, in some experiments con- 

 nected with the subject of dark 

 ground illumination, and have 

 worked out a device which 

 brings out new and most inter- 

 esting results. The accompany- 

 ing diagram will illustrate its 

 working. Let A, Fig. i, repre- 

 sent a sectional view of the tube 

 of an eye-piece ; B, a triple 

 achromatic lens of one inch 

 focus, and 30 degrees aperture ; 

 C, the diaphragm ; D, cap of 

 the eye-piece sliding over the 

 tube of the achromatic lens ; E, 

 a thin brass plate sliding be- 

 tween grooves in the top of 

 ^^°- '• the cap, having at the point 



F a small hole of not more than ^V^h of an inch in 

 diameter ; H, the cone of rays of the achromatic eye lens, 

 meeting at I. Place the thin plate -so that the hole F will 

 be at the side, and as near the apex of the cone of rays as 

 possible. It is quite evident that none of the light usually 

 used by the eye will be allowed to pass to it, as it will be 



