864 RECORD OF CURREMT RE>,EARCHES RELATING TO 



times sliow like deposits. A similar " sweating " almost invariably 

 occurs on our oculars, which has often been referred to an exudation 

 from the " black " within the tube, but erroneously. 



Mr. Kitton has in his i^ossession a small box of thin covers, selected 

 by the late William Smith, author of the ' Synopsis of British Dia- 

 tomacefc,' of which at least 30 per cent, exhibit traces of oxidation in 

 the form of minute pits. Query — Would not these covers have shown 

 the so-called " damping-off " if used ? 



Covering Fluid Mounts.* — In mounting objects in fluid, one of 

 the principal requirements is to fasten the cover of the cell securely, 

 so as neither to permit leakage nor runuing-in of the cement. There 

 are two methods described in most of the text-books, both of which 

 have, according to Mr. W. M. Bale, disadvantages that impair their 

 utility to a greater or less extent. 



The first, which is recommended by Davies, is to paint the cell on 

 its upper surface, and the cover on its under surface near the margin, 

 with thin coats of gold size or other cement, and to press down the 

 cover, forcing out the superfluous fluid in doing so, when the varnished 

 surfaces of the cover and cell, not being affected by the fluid, will adhere 

 together. It is a serious defect in this process that it will not permit 

 of sliding the cover to one side after fixing it, if, as frequently 

 happens, it should be necessary to readjust the position of an object 

 which may appear on examination under the Microscope to require 

 alteration. Moreover, thin pellicles of fluid frequently remain between 

 the cover and the surface of the cell, preventing the perfect adhesion 

 of the cement, and allowing the ingress of air. The other pro- 

 cess, which is preferred by Dr. Carpenter, is to simply apply the 

 cover upon a cell a little larger than itself, and when the outside is 

 dry to paint it round the margin with varnish, giving several coats as 

 they successively dry. This has the disadvantage of not holding the 

 cover sufficiently firmly to the cell, and of being peculiarly liable to 

 " running in." 



These evils are to a great extent obviated in the following plan, 

 which is especially adapted to cells of any thickness not greater than 

 that of ordinary card or thin glass. An essential point consists in 

 reversing Carpenter's rule, and using a cell smaller than the covering 

 glass, so that when the cover is in position it projects beyond the cell 

 for about one-sixteenth or one-twelfth of an inch on every side. The 

 cells may be made of any suitable material — thin tissue paper will 

 serve for minute objects, and common cardboard for those of con- 

 siderable thickness. The cell may be attached to the slide, or simply 

 placed in the position which it is to occupy, without being cemented. 

 The objects are immersed in the fluid in the centre of the cell and the 

 cover pressed gently down, forcing out the fluid which is in excess of 

 the capacity of the cell, and after it is ascertained, by examination 

 under the Microscope, that the object requires no readjustment, the 

 fluid must be removed from the space between the cover and the slide 

 outside the cell-wall. This is easily accomplished by simply allowing 



* 'Joiini. Micr. Soc. Vict.,' i. (1880) pp. 57-GO. 



