Examination and Study hy means of the Microscope. 235 



Suffice it to say that I prefer cells made of old japan gold-size, 

 which can be procured of dealers in microscopic materials. Within 

 such a cell, of sufficient depth and immersed in the preservative 

 fluid, a few of the diatoms, or a scraj) of the plant upon which they 

 are growing, is placed, and the glass cover fixed over it in the 

 manner described in the books upon manipulation. The filamen- 

 tous forms are thus preserved almost in their natural condition ; 

 but, on account of the presence of the endochrome, the sculpturing 

 of the silicious cell-wall is almost invisible. To show this 

 character, while the filamentous form is preserved, another method 

 of mounting is employed. A thin, clean covering glass is selected, 

 and laid upon a clean piece of paper. A large drop of distilled 

 water is then allowed to fall upon it, and in this drop the filamen- 

 tous diatom is thinly spread out. Then the cover is taken up by 

 means of a pair of forceps and held over the flame of a spirit lamp, 

 which has been turned down so as to be quite small and steady. 

 The cover is held some distance above the flame, and judiciously 

 manipulated, so that the heat is evenly distributed over it, and it 

 does not crack. As soon as all the water has been driven ofl" with- 

 out the formation of bubbles, the glass is brought gradually down 

 almost in contact with the flame, and held at that point for a few 

 minutes. Then the diatoms will be seen to turn black, on account 

 of the charring of the organic matter contained in them. After a 

 while this black carbonaceous matter will burn off, and they will 

 become quite white. If, however, there seems to be any difficulty 

 in burning off the last portion of carbon, the cover is lowered once 

 or twice to come in contact with the top of the flame, and then 

 raised again. In this way it will become red hot for a moment ; 

 and everything will be burned off except the silicious portions of 

 the diatoms. Now the cover is removed slowly from over the 

 flame, and held in the forceps until it is cold, but by no means laid 

 down upon any sui-face until it is quite cold, otherwise it will fly 

 into pieces. Then it can be laid upon an ordinary glass shde, and 

 examined to see if it is worth preserving, which may be done in 

 one or two ways : first, the glass cover is warmed, and a drop of 

 good spirits of turpentine let fall upon it, covering the diatoms. 

 Just before the spirits evaporate, a small drop of thin Canada 

 balsam is added, and a slide taken, warmed, and a drop of balsam 

 placed upon the centre part of it. Then the cover is brought down 

 upon the slide, the two balsam-covered sides together, in such a 

 way, by tilting the cover shghtly, that no air is allowed to come 

 between them, and the cover permitted to fall gradually into place, 

 driving a wave of balsam before it. In this way we have the 

 filamentous diatoms arranged as they grow, but with [endochrome 

 removed which would obscure the markings, and in balsam, which 

 renders them transparent. Some forms, as some of the 



