ZOOLOGY AND BOTANY, HICROSCOPT, ETC. 



859 



Examination of specimens by Coloured Light.* — Dr. M. Flescli 

 recommends the insertion of a neutral tinted slide in the Abbe con- 

 denser when examining sections stained with red and blue dyes. As 

 an example of the advantage may be cited the fact that some ganglion- 

 cells stained with Merkel's indigo and carmine mixture have a special 

 tendency to assume a blue colour, while others are stained red. This 

 difference is found to be augmented by tbe use of artificial illumination 

 and a neutral tinted slide. 



Again, in making an examination of sections stained with eosin 

 and hajmatoxylin, and where, owing to the thickness of the specimens 

 the eosin stain could not be recognized, a successful result was 

 obtained by using polarized light with a selenite plate, so placed that 

 the field of vision showed up yellow. The large cells impregnated 

 with eosin were thus seen to be of a red colour, while the blue nuclei 

 had apparently disappeared. 



Ahrens' Polarizing Prism. — Mr. Ahrens has recently added to 

 his prism f "a thin cover-glass at the end-face crossed by the line of 

 section, thereby making this line almost imperceptible as well as 

 affording protection against scratches. He has also found a new 

 method of cutting the prism by which there is extremely' little waste 

 of spar. 



Michel-Levy's Comparator. — M. Michel-Levy's Comparator (figs. 

 172 and 173) is based on the comparison of the colour of a crystal seen 

 under the Microscope with that given by a wedge of quartz producing 

 three orders of tints and which is taken as the unit of comparison. 



Fig. 172. 



At NN' fig. 173 are two Nicol prisms, between which slide the 

 quartz A and a diaphragm D. The rays reflected from the small 

 mirror are diverted at right angles by the prism C through the nicols, 

 quartz and diaphragm, and made parallel by the lens B, being then 

 reflected by the prism P through the eye-lens. To the hypothenuse 



* Zeitschr. f. Wias. Mikr., iii. (1886) p. 52. f See this Journal, ante, p. 397. 



