234 now to jyrepare Specimens of Diatomaceas for 



done by using a number of beaker glasses, of various sizes, in the 

 following manner : — Into a 1-ounce beaker the cleaned diatoms 

 are placed, and the vessel filled with water. It is then well stirred 

 up by means of a glass rod, and, after resting about five seconds, 

 poured off carefully into a 6-ounce vessel so as not to disturb the 

 sand which has settled. Again the vessel is filled up with water, 

 stirred, allowed to settle for the same length of time, and poured 

 into the same vessel. This is repeated until it has been done at 

 least six times, when we shall find all of the sand, free from diatoms, 

 in the small beaker. This can be thrown away, and as soon as the 

 material in the large beaker has settled it is returned to the small 

 one, and the same process gone through with, only extending the 

 time of settling now to about ten seconds. The next density is 

 that which settles in twenty seconds ; and so on, five or six densities 

 may be obtained, and if carefully prepared they will be found to 

 contain forms varying very much one from the other. The large 

 species of Triceratiiun, Aulacodiscus, and the like, will be found in 

 the coarsest density, and the broken diatoms in the lightest. 



Preserving and Mounting Sj^ecimens so as to have them in a 

 condition for study at any future time. — Of course, when possible, 

 Diatomacese should be studied in the Hving condition. But there 

 are many forms which have not been as yet found living, and these 

 can only be studied as dead skeletons; and, in fact, it is in the dead 

 skeletons of the Diatomacese that many of the most marked charac- 

 teristics are to be found; and on such characteristics sj)ecies have 

 been founded. Besides, the most beautiful sculpturing of the valves 

 is only to be seen after everything has been removed but the 

 silicious cell-wall I have termed the 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 silicious 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 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 creosote 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 pre- 

 paration of microscopic objects. The vessels in which the fresh 

 specimens of Diatomacese are put up are what are known to micro- 

 scopists as " cells," but how these are made cannot be gone into 

 here, as the description would occupy too much space and time. 



