222 



THE AMERICAN MONTHLY 



[December, 



eating and depositing a strong stony 

 structure at their base and sides. I 

 have observed a number of infant 

 polyps budding off the sides of the 

 group, and this usually occurs dur- 

 ing the autumn months. 



Examination and Exliibition of 

 Living Organisms. 



In studying minute, living speci- 

 mens of animal life it is often diffi- 

 cult to keep them alive for any con- 

 siderable length of time. Active, 

 free-swimming creatures, such as the 

 microscope reveals, find an ocean in 

 a little drop of water under the cover- 

 glass, and it is impossible to study 

 them carefully unless their move- 

 ments can be restrained. The water 

 evaporates from beneath the cover- 

 glass with such rapidity that some 

 means must be devised to prevent 

 drying. Ingenious devices of various 

 kinds have been described in the 

 Journal from time to time, by means 

 of which the evaporation may be 

 prevented. Perhaps the simplest 

 method of all, and one as satisfactory 

 as any of them, is this : Place a drop 

 of water containing the organisms on 

 a cover-glass of ^-inch diameter, and 

 invert it over a ring of wax or paraf- 

 fine on a slide. Then melt the wax 

 with a piece of wire to cement the 

 cover-glass and make an air-tight cell. 

 It is well to place a small bit of 

 Nitella or Anacharts, or some vigor- 

 ously growing alga in the drop of 

 water. In this way rotifers can be 

 seen to develop and multiply for days, 

 Cyclops, Daphnia, and other entomos- 

 traca will flourish in cells thus made. 

 To confine the movements of swim- 

 ming organisms, a little clean cotton 

 can be placed in the drop of water, 

 in the meshes of which they become 

 entangled, and are then readily kept 

 in view for two hours or more. The 

 plan is an admirable one when cyclo- 

 sis in a water plant is to be shown. It 

 is well known that cyclosis is always 

 most vigorous some time after the 

 specimen is prepared and allowed to 



remain undisturbed in its cell. Often 

 the movement is entirely stopped by 

 cutting, or otherwise preparing the 

 plant, and is not again active for an 

 hour or more ; in consequence of 

 which many disappointments occur 

 in attempting to show this phenom- 

 enon. But by putting the specimens 

 in such a cell a few hours before they 

 are needed, there need be no disap- 

 pointments. 



New Procass of Preparing 

 Diatoms.* 



BY PROF. W. BRUN. 



Prof. Brun has used the following 

 process for destroying the endo- 

 chrorae of diatoms with great satis- 

 faction. 



If the diatoms are freshly gathered 

 and still moist, add to them a few 

 crystals of potassic permanganate and 

 a very little water ; if they are dry, 

 pure or mixed with organic debris, 

 they are treated with a very concen- 

 trated solution of the same salt. 



The action of the salt should con- 

 tinue at least twelve hours. It is well 

 to stir the mixture occasionally in a 

 vial of about loo grammes capacity, 

 placed in a warm place, exposed to 

 the sun. 



The vial is then half filled with 

 water, and about 30 grammes of cal- 

 cined magnesia are added, and the 

 whole well shaken. After two or 

 three houlrs, pure hydrochloric acid is 

 added in portions of about one 

 gramme at a time, adding ten grammes 

 in ten minutes. 



For very delicate species, or those 

 having lime in their composition, the 

 action of the acid may be regulated 

 by using a larger quantity of water. 



With frequent agitation the action 

 of the chemicals is allowed to con- 

 tinue, aided by heat if necessary, un- 

 til the contents of the bottle lose their 

 color, after which the diatoms are 

 washed in the usual way. 



In this process we have first the 



* Bulletin de la Soc. Beige de Microscopie. 



