The Microscope. 207 



scope at a distance regulated by the intensity of the light desired . 

 In this position it leaves the way clear for the use of both hands in 

 the manipulation of the slide and the sub-stage accessories. The 

 heat and glare in the observer's eye may be readily overcome by the 

 interposition of a little screen so arranged as to shade the face. 

 Every microscopist can readily improvise such a screen. We have 

 found a piece of card-board stuck on an ordinary desk-file, composed 

 of an iron base and a vertical steel wire, to be very convenient for 

 this piu'pose. 



In the examination of diatoms and other objects by oblique 

 illumination, the lamp may be placed at the right of the observer at 

 a distance of about two and one-half feet from the microscope. 

 Some experts, in testing objectives, blacken the chimney of the lamp 

 and permit the light to pass through onTy a narrow slit. 



To make perfect the illumination of an Abbe sub-stage con- 

 denser, is in all cases desirable, and in bacteriological examinations 

 it is indispensable. With this condenser open, a cone of light having 

 an angle of divergence of 120° is brought to a focus upon the object. 

 Viewed with this intense light, the delicate contours of transparent 

 objects, which are made visible by differences of refraction, are 

 almost entirely lost, and the stained portions of the specimen, which 

 would be, without such a condenser, more or less concealed by the 

 outlines of the unstained portions, stand out in bold relief. This 

 "isolation of the stained image," as Koch terms it, is of great value 

 in histological study. An Abbe condenser should be a part of every 

 histologist's microscope. 



We notice that physicians are beginning to avail themselves of 

 the lantern to illustrate their papers on microscopical subjects. At 

 the recent meeting of the American Medical Society, some excellent, 

 views of diseased tissues were shown, and we notice that Dr. A. G. 

 Field, of Des Moines, recently entertained the Iowa State Medical 

 Society by a stereoptican exhibition of the microbes mentioned in his 

 paper before that body. This is an excellent method of impressing 

 an avidience with the idea that the author of an article knows what 

 he is talking about. We expect to see the lantern commonly used 

 for such purposes in the near future. 



Acknowledgments. — From Dr. W. M. Gray, Washington, D. C, 

 we have received a number of photographs taken by the two pro- 

 cesses, dry and wet, mentioned in his paper published last month. 



