ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 911 



hinged frames (also of cardboard) which cover the ends of the slides 

 and keep them in place. 



Chapman's Mould for Cells.* — This mould is a convenient im- 

 plement for making cells out of such plastic material as shellac, 

 sealing-wax, or paraffin. It consists of a cylindrical core, and a 

 removable collar concentric with it — both of brass. A rounded or 

 bevelled shoulder inside the collar shapes the top of the cell, and a 

 small shoulder on the core moulds a countersink suitable for the 

 reception of the cover-glass. As a single mould is intended for one 

 size and one depth of cell, several are necessary to an outfit. 



Selection and Preparation of Objects for Photographing.! — ^^• 

 G. M. Sternberg has found that success in making photo-micrographs 

 depends quite as much upon the selection of suitable objects and upon 

 their proper preparation with reference to photography, as upon the 

 optical apparatus used and the technical skill of the operator as a 

 microscopist and photographer, and he accordingly indicates the kind 

 of objects most suitable for making photo-micrographs, and the 

 methods of preparation which have given him the best results. 



Micrococci require a high power for their detection. When 

 properly stained, they may be photographed with a good 1/10 in. 

 objective ; but a higher power is better. The author has obtained his 

 best results by the use of the 1/18 in. homogeneous-immersion 

 objective of Zeiss. 



It is well to adopt a standard amplification for each class of 

 objects, so that they may be readily compared as to dimensions by a 

 simple inspection of the photo-micrographs made at different times and 

 places. The standard adopted by the writer for bacterial organisms 

 is 1000 diameters. A less amplification than this will not show the 

 smallest micrococci in a satisfactory manner, and a greater is not 

 necessary for a majority of the Bacteria. The method of mounting 

 bacterial organisms in general, for the purpose of photographing 

 them, is essentially to spread out a drop of the fluid containing them 

 upon a very thin and perfectly clean glass cover. This is allowed to 

 dry, and the bacteria are thus attached to the cover in a very thin 

 and tolerably uniform layer. 



The aim of the operator in preparing unicellular organisms or 

 vegetable and animal tissues for photography should always be to 

 secure a single layer of cells ; for when the cells are piled upon each 

 other, those in the background are necessarily out of focus, and 

 interfere with the beauty of the picture. 



Amcebce. — Especial attention is called by the author to the photo- 

 micrograph of an Amoeba from life, as it illustrates the fact that 

 transparent objects are the best suited for photography inasmuch as 

 they alone show interior details of structure in a satisfactory manner. 



Transparent objects which have a difl'crent refractive index from 

 that of the medium in which they are placed, do not usually require 

 to be stained ; for the increased photographic contrast which is obtained 



• Journ. N. York Micr. Soc, i. (1885) p. 188. 



t ' Plioto-micrographs and how to make them,' 1883, f.p, 91 117. 



