506 SUMMABY OF CURRENT RESEARCHES RELATING TO 



friable enough for manipulation after the operation has been repeated 

 once or twice. The mass must never be crushed as a large number of 

 species would be broken. 



For sorting and mounting the author uses a low objective (Zeiss aa or 

 Seibert No. 1) and a strong ocular. An iron hand-support is fixed to the 

 stage. A pig's or dog's eyelash fixed in a handle is used for picking out. 

 No prism is used as the eye and hand soon become accustomed to the 

 reversed position. 



The selected specimens are deposited in a small drop of glycerin-gum 

 lying on the surface of a cover-glass. The gum is made by dissolving 

 1 grm. of white powdered gum tragacanth in 50 grm. boiling distilled 

 water and then adding to the filtrate an equal volume of pure glycerin. 

 The cover-glasses should be 8-10 mm. in diameter and 1/10 mm. thick. 



The selected specimens are arranged on the cover by centering the 

 latter over a circle scratched on a slide. After having been washed with 

 distilled water, the covers are placed in an incubator at 100° (or water- 

 bath) in order to volatilize the glycerin, and hence fix the specimens to the 

 cover. 



For mounting diatoms, &c., the author uses balsam of tolu from which 

 cinnamic and benzoic acids have been removed by prolonged boiling in a 

 large quantity of w^ater. It is then dissolved in rectified benzine, filtered, 

 thoroughly dried, and finally dissolved in alcohol or chloroform. When 

 soft the index of this tolu is 1-68, and 1-72 when dry. When the 

 covers are quite dry the tolu thinned with benzine is added and finally a 

 drop of the thicker balsam. The slides are then dried in a stove at a 

 temperature of 60°-70° for an hour or two. 



The author decries the artificial (arsenical) media for mounting as the 

 formation of arsenious acid invariably takes place sooner or later and the 

 specimens become useless. 



Engelmann's Bacterium-method. — The controversy respecting the 

 value of this method for determining the intensity of the evolution of carbon 

 dioxide is continued by Pringsheim * and Engelmann,f to which Prings- 

 heim | again replies. 



Cleaning" Diatoms.§ — Mr. A. L. Woodward gives the following as an 

 easy and efiective method : — 



Coarsely powder the diatom-bearing earth, or the dried diatomacese, 

 and mix with 6i-sulphate of potash. Take a porcelain gallipot, about an 

 inch high, and fill it about one-third full of the mixture of diatoms and 

 bi-sulphate ; take the tongs and set it down among the glowing coals in 

 the stove. The bi-sulphate immediately begins to fuse, and boils up as 

 black as pitch. If the gallipot is not too full it will not boil over, but 

 rises up and sinks back again and again until, as the sides of the pot begin 

 to turn red the boiling mass becomes clear, and the bottom of the vessel is 

 seen glowing hot through it. When the boiling ceases, lift out the pot and 

 let it cool. Brush off any dirt or ashes that may be on the outside of the 

 pot, and then jput it in clean, hot, soft water, and let the contents dissolve, 

 which they will soon do. Pour off the water, and replace with clean, soft 

 water, repeating this several times to get rid of the acid. Then shake up 

 in a test-tube, let the sand settle, and pour off the diatoms, repeating this 

 process, also, if necessary. 



In the author's hands this process has given very fine results, and 



• Ber. Deutsch. Bot. Gcsell., iv. (1886) Gen. Vcri?amm]., pp. xc.-xcvi. 

 t Bot. Ztg., xlv. (1887) pp. 100-10. J Ibid., pp. 



§ Rcir.'titif. Enquirer, ii. (1887) pp. 70-1. 



200-4. 



