ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 145 



case of the marine or fresh-water diatoms, a final bleaching may be 

 accomplished by pouring the diatoms, while still in acid, into a shallow 

 and contracted glass or china saucer, and adding thereto a few drops of 

 Darby's prophylactic fluid, which actively effervesces and liberates the 

 bleaching gas. While the boiling alone, first in sulphuric acid and 

 later adding some nitric acid will be sufficient, yet a greater whiteness 

 is produced by the addition of the prophylactic fluid as a bleaching 

 substance. 



The boiling process above described dispenses with the addition 

 during the cleaning of any powdered crystalline salts, and is also 

 operated with a minimum of acid fluids, and to purify the diatoms from 

 acids, it is merely necessary to allow the preparation to settle a few 

 minutes and carefully draw off the bulk of the acid and allow the 

 diatoms to settle in shallow china saucers, 1/2 in. preferably; draw 

 off and change the water after one minute intervals, and repeat for four 

 changes. A trial test made on a slide, dried over a flame, will show that 

 'all acid has been removed from the diatoms. At this stage there is a rich 

 concentration of the diatoms, but included therein some sand-grains and 

 flocculent soil ; the flocculent matter is removed by repeated shakings 

 and settlings through a few inches in depth of clean water at three 

 minutes intervals, until when tested under the Microscope a satisfactory 

 appearance is reached. The acid-cleaned diatoms are again transferred 

 to the crystal gigging-glass and water added, and then very gently 

 gigged for a final concentration of the diatomaceous forms and a further 

 portion of fine sand removed. The finishing touch to the cleaning for 

 concentration of the forms is done by placing a small quantity of the 

 acid-cleaned and concentrated diatoms into a concave black or dark glass, 

 such as is used in tourists' eye-glasses, and the contents gently oscillated 

 from side to side and to and fro, when the diatoms will be found richly 

 aggregated on the centre of the containing glass. The glass is then 

 tilted and the diatoms removed by the gentle suction of a pipette, the 

 dark glass enabling the mass of diatoms to be distinguished from the 

 fine grains of sand adherent to the bottom of the glass. In lieu of the 

 dark concave eye-glass, a deep bull's-eye watch-crystal makes a good 

 substitute for the final act of concentration. 



Diatoms are also richly concentrated from sand by simply spreading 

 the containing fluid over either a six-inch square of smooth or ground 

 glass, and gently gigging it while tilting it in the direction of one of 

 the corners and allowing the fluid to run off into a proper receptacle. 

 A large percentage of the sand-grains remain in situ, or adherent to the 

 glass surface. 



The author refrains from alluding to boiling in alkaline solutions to 

 neutralize traces of acids as he has not found it desirable or necessary 

 to do so ; nor does he refer to flannel or silk strainers for the final 

 cleaning and separation of diatoms. 



Birch, H. — Ueber Ziichtung von Spaltpilzen in gefarbten Nahrmedien. (On the 

 cultivation of Schizomycetes in coloured media.) 



Tagebl. 60. Versamml. Deutsch. Naturforscher u. Aerzte, 1887, pp. 275-7, 

 Raskin, M. — Zur Ziichtung der pathogenen Mikroorganismen auf aus Milch 

 bereiteten festen und durchsichtigen Nahrbbden. (On the cultivation of patho- 

 genic micro-organisms on solid and transparent media prepared from milk.) 



St. Petersb. Med. Wochenschr., 1887, pp. 357-60. 



1888. L 



