1899] MICROSCOPICAL JOURNAL. 61 



This must be previously focused on a scratch or on a 

 fly's wing- placed on the inside surface of a plane glass. 

 If you prefer using ground glass, make a small pencil cross 

 on it, and then you cement over this, by means of Canada 

 balsam, a thin microscopical cover-glass ; then focus the 

 aerial image till it is as sharp as possible. A large number 

 of the invisible rays can be cut off by interposing a tank 

 made of two pieces of glass, like a magic-lantern tank,filled 

 with a weak solution of fluorescine between the light and 

 the microscope. Perhaps other fluorescent substances 

 like quinine would answer. The photographic objective 

 must be removed, and the microscopic objective used alone; 

 but with a short camera an eyepiece is an advantage. The 

 proper one is a projection ocular, but the ordinary one will 

 often answer ; they, however, vary in performance. As 

 microscopical objects are seldom flat, and as the objectives 

 have little depth of focus, the image is always indistinct 

 at the edges ; for this reason only the central part of the 

 image is used. It is necessary to have the light and con- 

 denser quite central with the objective. It is advantage- 

 ous to lengthen this quarter-plate camera by means of a 

 cone of paper, blackened inside, fastened on to the front. 

 Be careful to fix the camera firmly to the table by a clamp 

 or weights, to avoid shaking it when putting in the slide, as 

 the image is easily thrown out of focus. — Eng. Mechanic. 



MICROSCOPICAL MANIPULATION. 



"Method of Fixign Blood for Microscopic Study." — I 

 note in your December issue under this heading, that dis- 

 satisfaction is expressed with the ordinary method which 

 is employed for obtaining slides, viz., the placing of two 

 cover glasses together and then pulling them apart. For 

 a number of years, I have tried this method and it is on 

 very rare occasions that I have succeeded in obtaining a 

 satisfactory spread. Some years ago, while working with 

 Professor Ewell in measuring blood corpuscles, we obtain- 

 ed easily and quickly a large number of specimens in the 

 following- manner: The blood-drop taken from the ear or 



