536 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Another plau is suggested * as an alternative to the ordinary one of 

 placing a small quantity on the slide and then ajiplying the balsam. 

 Pour into a test-tube a sufficient quantity of Canada balsam to mount 

 as many slides as may be required, and heat over the flame of a spirit 

 lamp. When the balsam becomes thin, dredge into it through muslin 

 the starch to be mounted. The air-bubbles must be burst either by 

 again heating the balsam, or by diluting it with turpentine. The 

 starch may then be mounted by taking up a small quantity with a 

 dijjping tube, and placing upon a glass slip, and covering with a thin 

 circle or square previously warmed 



Mounting Desmids.t— Dr. M. C. Cooke, in dealing with the sub- 

 ject of mounting desmids for the Microscope, considers that the pre- 

 servation of the eudochrome and its colour is a matter of minor im- 

 portance. For scientific j^urposes the empty frond is often of superior 

 value to one filled with endochrome, as it permits the punctae or 

 markings of the segments to be seen, which are obliterated whilst the 

 endochrome remains, and in the genus Cosmarium this is of greater 

 importance than ever. 



For the study of the endochrome alone its j)resence is of course 

 most important ; but this can be done, and drawings made from the 

 plant in the living state, and if si^ecimens can be mounted with the 

 endochrome unchanged and uncoutracted, so much the better, but no 

 method has yet proved entirely satisfactory. Dr. Cooke kept some 

 slides for twelve years mounted in silicates of potash and soda, but 

 half of them deliquesced. Mr. Wills, however, kept slides much 

 longer by simply using the water in which the Desmids were collected 

 and never leaving them exposed to the daylight. 



One great difficulty in mounting objects with such thin and deli- 

 cate cell-walls as desmids is to employ a medium of no greater 

 density than the cell-contents. If a denser medium, such as glycerine, 

 be used, the endochrome immediately contracts, and never expands 

 again as before. Water, or water containing a little camphor, is of 

 equal density, and no change can be detected. 



After all, the preservation of the endochrome is of less importance 

 than the jierfect contour of the cell. If there is any contraction or 

 collapse, the objects are useless. Supjiosing, therefore, that thei-e is 

 no necessity to preserve the endochrome, there is another feature to 

 remember besides the preservation of contour, and that is, that the 

 medium employed should not render the delicate cell-walls so trans- 

 parent as to become ultimately invisible. In simple water Dr. Cooke 

 found no difficulty in discerning the structure of the cell-walls after a 

 period of not less than twelve years. So much cannot be said for gly- 

 cerine. Empty fronds, both of desmids and Volvox, stained of 

 various colours, exhibit all the details in an unexceptionable manner. 



Wax for Dry-mounting Opaque Objects.^ — Mr. H. J. Eoper 

 uses mahogany slides, 3 inches by 1 inch, with central circular cell 



* 8ci.-Gossip, 1881. p. 88. 



t Jouin. Quek. Micr. Club, vi. (1881) pp. 203 II (4 pis.). 



; Ibid., pp. 193-3. 



