96 



contrivance as the Gairdner microscope, described by Dr. Car- 

 penter, or improved by Mr. J. N. Tomkins.* Dr. Arnott in- 

 forms me that he uses two Coddington lenses, one of 66 diame- 

 ters, and one of 180, generally using the former only. In this 

 way we may at once tell what is worth retaining, and what should 

 be rejected. Gatherings are, however, always examined with 

 the compound microscope soon after we get them home ; the 

 movements of the Diatoms in their living state may then be 

 observed, and the presence and position of the endochrome noted. 

 To study the reproduction of these plants they must also be ob- 

 served in the recent living state, as no method of mounting known 

 will preserve, in their natural condition, the characteristics of this 

 interesting and important part of their natural history. 



If we wish to mount the Diatoms simply to show that they are 

 Diatoms, and to surprise the uninitiated, nothing is easier ; we 

 have but to boil them for some time in nitric acid, wash them 

 with water, and place a small quantity of the sediment on a glass 

 slide, and dry it over a spirit lamp. When it is dry, and still hot, 

 we drop upon it a small quantity of Canada balsam, and place 

 over it the previously prepared thin glass cover and press it 

 down. When the balsam is sufficiently hard, the superfluous 

 portion which has exuded around the cover is removed with a 

 penknife, and the slide is cleaned with alcohol ; this latter being 

 far superior to turpentine, which the European (and more espe- 

 cially English) microscopists use, on account of the high price of 

 alcohol. The above process is extremely easy to manipulate, but 

 it will never satisfy a student of the Diatoms.; for, though it is 

 sufficient for fossil and sub-peat deposits, it would never do for 

 the purpose of illustrating genera and species, for which Diatoms 

 should be prepared and mounted. We therefore proceed to show 

 how they may be mounted so as to satisfy a student, and render 

 permanent their characteristics, so that they may, at any future 

 time, be exhibited and studied. 



We shall require, in the first place, a quantity of glass slides, 

 of the dimensions of on,e inch wide by three inches in length. 

 These should be of as white glass as possible, and ground on the 

 edges so as to give them a neat and finished appearance. Only 

 such as are free from scratches, or other blemishes, in the central 



* Mic. Jour. Vol. VII. p. 57. 



