140 SUMMARY OP CURRENT RESEARCHES RELATING TO 



diamond point just touches ] the cover-glass. By moving the point out 

 eccentrically, a circle may be scratched on the cover-glass with com- 

 parative ease. This device can be employed with advantage for alg39 

 mounted in glycerin jelly, but is not to be adopted for wet mounts, 

 because small objects are easily moved out of position. 



If several specimens are to be mounted together, the author advises 

 the use of a capillary tube bent at an angle of 120° about 2 cm. from 

 the end of the tube. Then under a magnification of about 100 the 

 desired specimens are sucked up by capillary action, and the process 

 repeated until a sufficient quantity have been obtained. 



For collecting DesmidiacesB the author uses a syringe of the following 

 construction : — A thick glass tube about 2 cm. wide and 30-40 cm. long 

 is closed in front with a cork, through which passes a short fine tube of 

 glass terminating in an opening of 1-2 mm. in diameter. It is advised 

 to have several of these points, and that some should be bent at an angle 

 of 90°, as this angularity is often convenient. The piston is plugged 

 with tow and thread. 



Owing to the influence of light on DesmidiacesB and on Yolvociniee, 

 these objects may be successfully separated if the vessels containing 

 them be exposed to sunlight in such a way that they are protected from 

 the direct rays. In a day or two it will be found that many forms will 

 crawl out of the mud towards the light side, where they may be collected. 

 A pure sample of Volvox may be frequently obtained by placing a small 

 quantity of the material in a pipette, and then placing the pipette point 

 end upwards against the window. In a few minutes the Volvocinise will 

 be found at the top, from whence an almost pure collection can be expelled. 



For ringing round preparations mounted in glycerin-gelatin the 

 author advises the employment of amber-lac dissolved in linseed oil. 

 Put on in thin layers it is quite transparent, and allows the use of 

 immersion lenses. 



Heydenreich's cement, although it has excellent points, has the 

 disadvantage of requiring to be stained, and the dyes used for this 

 purpose gradually work into the preparation. For completing the 

 fastening down, the author formerly used equal parts of colophonium 

 and yellow wax. To this he now adds to every 10 parts 1-2 parts 

 linseed oil and 1 part of Canada balsam. This is put on warm. 



Mounting Fresh-water Algse.* — Dr. L. Klein mounts fresh-water 

 algse in glycerin or glycerin-gelatin. The author uses the former for 

 very small objects, and adopts for this purpose the technique proposed 

 by Migula. A drop of 1 per cent, osmic acid is run under the cover- 

 glass, and in ten to twenty minutes afterwards the glycerin. In order 

 not to blacken the oil-drops, &c., the osmic acid is added in as small 

 quantities as possible, and this is best done by blowing it under the 

 cover-glass through a capillary tube. In all other cases the author uses 

 glycerin-gelatin, which, with the proper precautions, is an excellent 

 imbedding material. The object is first hardened by exposing it as a 

 hanging-drop to the fumes of the acid for a few minutes. It is then 

 placed in one or two drops of dilute glycerin, and the surplus having 

 been drained off or the water evaporated, a drop of glycerin-gelatin pre- 

 viously heated in a test-tube is dropped on by means of a fine glass tube. 

 By this device air-bubbles are avoided. 



» Heclwigia, 1888, pp. 121-6. 



