H. MORLAND ON MOUNTING DIATOMACEJ2. 325 



diatoms selected and put on one side I set a day apart for 

 mounting them. (I may here say that I invariably mount by 

 daylight, as I think it is less trying to the eyes than lamp-light, 

 more especially when persevered in for some hours together.) 

 I begin by first transferring as many of the diatoms as I may 

 require on to my "mounting slip," placing them about half-an- 

 inch to one side of my ruled-glass disk in an inked square or circle 

 so that they can be readily found when wanted. I now attach a 

 cleaned cover-glass to the upper surface of the ruled-glass circle ; 

 this I do by breathing on it through the short piece of glass 

 tubing already described. Xote that I breathe on the cover I 

 intend using, and not on the ruled circle on my " mounting 

 slip." On turning the cover over and pressing it down on the 

 ruled glass on slip it will adhere sufficiently firmly and long for 

 all practical purposes. Placing my slip under my microscope I 

 now take up the "selected" diatoms one by one and arrange 

 them on the cover-glass as desired. It is, however, sometimes 

 needful to pass these diatoms through a drop of water under the 

 microscope in order to free them from dirt or particles of 

 broken diatoms. 



"When arranging the diatoms care must be taken that if the 

 diatoms have a concave side the same be not placed next the 

 cover-glass, as in such case a bubble would be formed there 

 when the styrax was applied, with the result that the diatom 

 would inevitably be dislodged. When the diatoms are arranged 

 satisfactorily all that is now necessary to fix them is simply to 

 breathe upon them gently through the " breathing tube," watch- 

 ing them through the microscope at the same time. The 

 moisture of the breath is condensed on the cover-glass and 

 causes the diatoms to adhere closely to the same ; the breath- 

 ing must not be continued too long, as otherwise the excess of 

 condensed moisture will very often cause the diatoms to float 

 and get displaced. The moisture can easily be dried up again 

 by simply drawing the breath through the tube. The " mount- 

 ing slip ' is now placed on the turntable and carefully centred, 

 when a small " guide ring," about ■— inch in diameter, can be 

 traced round the arranged diatoms with a mixture of gum and 

 some colouring matter, such as lamp-black, which is not apt to 

 fade as do the aniline colours. The slip intended for use with 

 the cover can also be ringed now on the wider side, as this ring 



