ZOOLOaY AND BOTANY, MICBOSCOPY, ETC. 307 



the current is weak, whidi can be well regulated by the shape of the 

 blotting-paper, the animal keeps its position unaltered ; and as by 

 the absorption of the water the cover-glass exercises greater pressure 

 upon the slide, there is less danger of losing the animal from the 

 field. Then add to the opposite edge of the cover-glass by means of 

 a glass rod a drop of 1/2 per cent, osmic acid, which immediately 

 penetrates to and kills the animal without altering its shape. In the 

 same way are added to the preparation the different alcohols, 15, 45, 

 90, up to 100 per cent., whereby the animal obtains the required 

 hardness. Then follows the staining with picro-carmine or methyl 

 green (which have proved to be the best for Protozoa). In the same 

 manner, after 5-7 minutes the stream of colour is replaced by weak 

 alcohol (50-30 per cent.), when the whole preparation is complete. 



This method is very simple and very quick, the whole manipulation 

 lasting 7-12 minutes, so that the preparation is finished in a quarter 

 of an hour. Care must be taken to have the object always in sight, 

 and not to keep up too strong a current. 



The stained object can be well examined in the weak alcohol, and, 

 if the blotting paper is removed, can be kept whole hours in it. The 

 manipulation is well adapted for drawing with the camera; but to 

 make a permanent preparation, it must be treated with a clearing 

 fluid, glycerine, oil of cloves, &c., and finally with Canada balsam, 

 which, dissolved in benzine, is quite thin and liquid. The applica- 

 tion of the clearing fluids is the chief difficulty in the preparation, 

 because the absolute alcohol flows through quicker than the liquids 

 which follow, which gives rise to small air-bubbles between the two 

 liquids. " It is, of course, obvious that the preparations often do not 

 come up to the requirements of our day, especially as regards beauty. 

 For, beside the objects prepared, there are a number of algse, infusoria, 

 mud, &c., in the preparations, by which they are made more or less 

 dirty." 



Arranging Diatoms.* — E. H. Griffith thinks that those who wish 

 to arrange diatoms will find the following of great assistance : — 



With a pipette place the diatoms on a film of mica, as the mica is 

 very thin, and when mounted can instantly be heated to an intense 

 heat over an alcohol lamp. With a pair of scissors cut small strips 

 from the best part of the diatom field of mica, moisten the mica on 

 the other side and lay it on the prepared slide near the centre of the 

 slip to be used, or if the diatoms are to be mounted on a cover-glass, 

 place the strip near it, and with a pen make a delicate dot of ink on 

 the under side of the slide to mark the place for placing the diatom. 

 From the mica the diatoms can be very easily picked, while from the 

 glass sometimes it is almost impossible to pick them. Several strips 

 of mica may be placed side by side with different kinds of diatoms if 

 desired. 



Instead of putting the diatoms on a cover-glass and the cover- 

 glass on a metal strip, in order that organic matter may be burned 

 away over a spirit-lamp, put them with a pipette on the end of a thin 



* The Microscope, iii. (1883) pp. 205-6. 



