ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 1079 



fresh layers, and it must be always kept in mind that once allowed 

 to dry the whole cultivation is ruined. 



In most cultivations a constant change of the varieties takes place, 

 one form driving out another, and this in its turn being supplanted 

 by a new variety. As a rule the more motile forms spread over the 

 less mobile, and the former may therefore be easily removed by means 

 of a brush. 



Mounting Diatoms.* — Senor A. Truarn y Luard gives, in his 

 work on the diatoms of the Asturias, a new and original method^ for 

 mounting. 



Egg-albumen is mixed with its own weight of distilled water, and 

 with 5 grins, of pure ammonia. The mixture having been beaten to 

 frothing, is allowed to stand for 12 hours. The clear fluid is then 

 decanted, filtered, and preserved. The addition of ammonia prevents 

 decomposition for a period of one or two months. Coating the cover- 

 glass with the fluid, arranging the diatoms, and fixing them by breath- 

 ing over them, is performed with exactitude by the use of this gelatin 

 solution. To close the preparation, the cover-glass is placed on a 

 metal plate, and heated to a degree sufficient to coagulate the albumen. 

 Preparations obtained by this method are extremely clear and 

 brilliant. 



Mounting Isthmia.| — Mr. E. Hitchcock, in reference to a 

 remarkably puie gathering of Isthnia nervosa attached to seaweed, 

 points out that by the exercise of some skill and patience their 

 natural beauty may be brought out far better than is often seen ; 

 and he remarks that there is " a fine art in mounting microscopic 

 objects that many of the more stolid investigators affect to despise ; 

 but so long as the specimens are not distorted, misshapen, or crushed 

 out of their natural condition, they lose nothing for purposes of 

 study by being skilfully prepared for exhibition." 



The usual method of mounting Isthnia is by drying the frustules, 

 either on the seaweed or, freed by shaking, on an opaque ground. In 

 this way, exercising some care in selecting the most showy groups, 

 very attractive specimens can be obtained. A dry mount of the free 

 frustules can be greatly improved by previously clearing them, or 

 rather removing the dried endochrome. The best way to do this is 

 to place them for a few minutes in a bleaching solution which may 

 be chlorine w r ater, Labarracjue solution, or any such active agent. No 

 acid is required. In the course of fifteen minutes the frustules will 

 probably be quite white, and, owing to the air contained in them, 

 they will form a perfectly pure layer floating at the top of the fluid. 

 It is then only necessary to remove the solution below by means of a 

 pipette or siphon, wash several times with water, drawing it off in 

 the same way, and finally collecting the diatoms in a bottle with some 

 alcohol for preservation. They are now perfectly clean, and white 

 as snow. 



To prepare a dry mount select a clean cover-glass and place a 



* An. Soc. Espafi. Hist. Nat., xiii. (1884) pp. 307-Gi (4 pis.). 

 t Amer. Mon. Micr. Journal, vii. (188G) pp. 148-9. 



