INVERTEBRA.TA, CRYPTOGAMIA, MICROSCOPY, ETC. 1043 



light by floating corpuscles in tlio background. And this difficulty 

 led him to invent the following culture-slide. 



A circular hole, about \ inch in diameter, is drilled through the 

 centre of a glass slide. A very thin circle of cement, ^ inch in 

 diameter, is then turned about this central hole on one side of the 

 slide, and a thin glass cover is attached to it by gentle pressure. 

 When the cemeiit is thoroughly dry, the cell is ready to receive 

 the drop of blood, or other fluid which is to be observed. This is 

 placed in the bottom of the cell (a, Fig. 114), and flows by capillary 

 attraction into the space below, between the thin cover and the slide, 

 until it extends to the circle of cement by which the cover is attached. 



Fig. 114. 



he be 



We have thus a thin stratum of the fluid between the points 6 and c, 

 which may readily be examined by inverting the slide and bringing an 

 immersion lens down upon any point between the central air-chamber 

 and the circle of cement by which the cover is attached. Finally, the 

 cell is closed by turning a still larger circle of cement upon the upper 

 surface of the slide, and attiching a larger thin glass circle (d). 



Mr. Sternberg docs not sec why it should not also serve a good 

 purpose as a cell in which to mount objects either dry or in fluid. If 

 the manufacturers would furnish glass slips of diflcrent thicknesses, 

 having central perforations of :j to ^ inch in diameter, a thin glass 

 cover can easily be attached to make the bottom to the cell ; and 

 these might, for many purposes, replace the various cells in common 

 use. 



Apertures exceeding 180° in Air. — Mr. Shadbolt's note on this 

 subject will be found in the Proceedings of the November Meeting, 

 infra, p. 1080. 



Visibility of Minute Objects — New Medium for Mounting 

 {Monohromide of Naphthaline). — Professor Abbe has recently been 

 experimenting upon substances adapted for mounting diatoms (having 

 regard to the suggestions made in Mr. Stoi»henson's recent paper *), 

 and has discovered that monohromide of naphthaline is very suitablo 

 for the purpose, and does not present the inconveniences of some of 

 the other substances. 



Tlio liquid is colourless and oleaginous, with the odour of naph- 

 thaline. It is soluble" in alcohol and otlicr, and has a density of 

 1*555, with a refractive index of l-r)5(S, giving therefore as tho 

 " index of visibility" 22 as against 11 for Canada balsam. It is not 

 volatile. 



Dr. II. van Ileurck refers to this substance, some of which was 

 sent him by Mr. Zeiss. His experiments with it have given tho l>est 



• Sec this Joiirnnl, antr, p. ^^CtX, 



