704 SUMMABY OF CURRENT RESEARCHES RELATING TO 



of oxide of zinc in gum-water and then put on the finishing coating 

 afterwards. 



Wax Cells— Decomposition of Glass. — Herr E. Weissflog of 

 Dresden writes to Professor Hamilton L. Smith * that he considers 

 that wax cells must be thrown aside. He has a number of preparations 

 of diatoms from Eulenstein made with wax cells which are completely 

 spoilt and the covers loose. Herr Lindig of Dresden, who has had 

 much experience in mounting, and has for many years endeavoured to 

 find some reliable cement, has arrived at the result that shellac is the 

 best, and he now uses nothing else. 



At the same time, Herr Weissflog is decidedly of opinion that the 

 spoiling of preparations is partly due to the glass. He has slides of 

 the best plate-glass, and when they ai-e packed away the outer surface 

 appears after a time covered with moisture. He has also often found 

 numerous crystals on Chance's cover-glass, which appear to come from 

 a kind of sweating or decomposition of the sm-face. 



Arabin for Mounting.! — Mr. H. J. Waddington says that "arabin," 

 or gum arabic from which all impurities have been removed, will be 

 found valuable to microscopists for attaching diatoms, &c., the ordinary 

 gum arabic presenting a granular appearance. 



To obtain arabin for microscopical use clear and white gum arabic 

 should be selected, and dissolved in distilled water to the consistency 

 of thin mucilage. On filtering and pouring the filtrate into rectified 

 alcohol, well shaking it, the arabin separates as a white pasty mass. 

 It must be placed on filter paper and washed with alcohol (not 

 methylated spirit) until the washings are free from water and the 

 alcohol comes off as pure as it went on. Allowed to dry, the mass 

 (other than the edges of the surface) will be a perfectly pure white 

 powder. Though troublesome and expensive to prepare in consequence 

 of the quantity of alcohol required, a little of it goes so far that prac- 

 tically it costs little. 



For use the arabin should be dissolved in distilled water to any 

 required consistence, and passed twice through filter paper pre- 

 viously washed with distilled water. It may then be placed on the 

 slips, drained, allowed to dry, and the slips put away for use. In 

 this condition and with ordinary precautions it may be preserved 

 indefinitely. 



Mounting Diatoms in Substances of High Refractive Index.— 

 In confirmation of Mr. J. W. Stephenson's views on this subject, | 

 Professor Hamilton L. Smith § reports that slides of Amphipleura pellu- 

 cida, P. angulatum, and Bhizosolenia styliformis, mounted in mono- 

 bromide of naphthaline (re£ ind. = 1*658) by E. Weissflog,] | show 

 that there is very little difference, in regard to the visibility of such 



* See Amer. Mon. Micr. Journ., ii. (1881) p. 49. 



t Journ. Quek. Micr. Chib, vi. (1881) pp. 199-200. 



j See this Journal, iii. (1880) p. 564. 



§ Amer. Mon. Micr. Journ., ii. (1881) p. 49. 



II See this Journal, ante, p. 151. 



