BY UHKIHTOPHEB JOHNSTON. L6 



materially mar the beauty of the preparation. This defect may 

 be easily remedied by quickly washing out the alcohol; after 

 which the even display of the diatomaceous forms is readily 

 accompli shed, especially if we give the end of the slide a fillip 

 with the finger previous to putting it aside to dry spon- 

 taneously. At this point the micrbscopist has the election either 

 of mounting in the dry way, or of embalming his tiny treac 

 in (' mada balsam. He may add the balsam drop an natun and 

 gently heat over a spirit-flame before applying the cover, or he 

 may omit the evaporation and mount "soft," placing a small 

 screw, for a weight, upon the cover, or he may use balsam 

 thinned by chloroform, or dissolved in absolute alcohol, and 

 filtered, as recommended by Dr. Schaeffer, of the Army Medi- 

 cal Museum, and then apply the continuous pressure of a small 

 weight. By the first method the slide will be immediately 

 ready for use when labeled; by the others, a certain number of 

 hours or days must elapse before the margins of the covers will 

 have become securely attached. But the work is done, and the 

 student may now gloat over the things of beauty which he 

 views by the light of science. It is true that he may regret a 

 few forms which have been floated off under the descending 

 cover; but careful manipulation alone will in future prevent 

 this mishap. But how can he imitate the exquisite group 

 of the Diatomaceen-Typen- Platte of Moller? He may not equal, 

 but he may, with much practice, approximate to the excellence 

 of that wonderfully skilful preparer by arranging his Diatoms 

 dry upon a slide or cover previously coated with a thin film of 

 gelatine, and then fixing them by exposure for a moment to the 

 vapor of distdled water. In mounting with balsam the 1 tiatoms 

 Cannot change position, but the gelatine disappears, and ifl 

 no more forever. 



Before closing this paper, perhaps already too long, we deem 

 it germane to the subject to refer to the plan which we have 



adopted with success in the sehvtion or picking out <>f particu- 

 lar Diatoms. It may not be altogether original, yet it is prac- 

 tical, and may aid the inexperienced. 



Nothing is i lasier than to seize particular diatoms and transfer 

 them to a bottle for future use, or to a slide, provided the field 

 from which we select be rich and clean. Difficulty, however, 



