NATURAL HISTORY OF THE DIATOMACE^E. 497 



thincr has been removed but the siliceous cell-wall I have termed the 



o 



skeleton. Therefore I advocate the cleaning of a portion at least of 

 every gathering in the manner described, so that nothing will be left but 

 the clean siliceous cell-wall. 



If we desire to keep specimens in a state as near that they present 

 when living as possible, we have to put them up in some preservative 

 fluid in which they will not decay, and in which the softer parts will be 

 preserved. Unfortunately these soft parts do not keep well; but the 

 fluid which I have found to be the best for the purpose is distilled water, 

 which has to every fluid ounce two or three drops of wood creosote 

 added, and thereafter a sufficient number of drops of alcohol, which will 

 be about double the number of the drops of creosote, to make the creo 

 sote soluble in the water, which it is only to a very slight degree under 

 ordinary conditions. I do not advocate any fluid containing glycerine, 

 or, in fact, any of the preservative fluids described in the books treating 

 of the preparation of microscopic objects. The vessel in which the 

 fresh specimens of diatomaceae are put up are what are known to micros- 

 copists as &quot;cells,&quot; but how these are made cannot be gone into here, 

 as the description would occupy too much space and time. 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 scrap 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 filamentous forms are thus preserved almost in 

 their natural condition; but, on account of the presence of the endo- 

 chrome, the sculpturing of the siliceous 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 filamentous 

 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 

 VOL. i. 65 



