NEW PHOTO-MICROGRAPHIC APPAEATUS. 101 



viewed with an ordinary eye-piece. Having completed the adjust- 

 ment, the eye-piece is removed and a projection eye-piece inserted. 

 The camera is now slid up to its place, but leaving enough room 

 for the fingers to adjust the eye-lens of the projection eye-piece. 

 This is moved until a sharp outline of the diaphragm in the eye- 

 piece is produced upon the grey glass screen or upon a piece of 

 white paper held near the end of the camera. The camera is now 

 pushed up until the front tube enters the light-excluding cap 

 fitted on the microscope tube, and then extended until the 

 desired size of the picture is obtained. The object should now 

 be accurately focussed upon the plate-glass screen, a good focus- 

 sing glass, of course, being used. 



A very good method of judging exposure is given in Mr. E. C. 

 Bousfield's " Guide to the Science of Photo-Micrography," with 

 table for use in conjunction with Warnerke's sensitometer. 



Artificial Serum. — An improved formula for artificial serum 

 may prove useful to those who make daily examinations of the 

 blood. Dr. Mayet, of Lyons, who is himself an expert microsco- 

 pist, recommends the following composition : — Distilled water, loo 

 grammes j anhydrous phosphate of sodium, 2 grammes ; sugar, 

 q.s., to bring the solution up to sp. gr., i"o85. This hquid 

 appears to be an excellent medium for preserving blood-cor- 

 puscles and other globular anatomical elements without alteration 

 for a considerable time, so that they may easily be counted and 

 examined under a high power in anaemia, leucocythsemia, etc. 

 Owing to the density and slight viscosity due to the sugar, and the 

 preserving action of the alkaline salt, the ditt'erent elements are 

 prevented from adhering together, and remain thus equally 

 distributed in the fluid. 



Potassium Cyanide Vapour. — -It is a mistake to suppose, 

 says the Scientific Neivs, that the vapours given off by potassium 

 cyanide are deadly to all animals. We have seen several species 

 of beetles which, after prolonged imprisonment, along with abun- 

 dance of this chemical, came out quite safe and sound. 



