ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 453 



A drop of balsam, about the size of a grain of pepper, is placed on 

 the slide, and the latter put, with the halsam on the under side, on a 

 horizontal plate pierced with an aperture 4 cm. in diameter, and 

 allowing of movement to the extent of about 10 cm. up and down by 

 means of a rack and pinion. The spirit-lamp is put below the aper- 

 ture in the plate, and consequently underneath the drop of balsam on 

 the slide. 



The flame of the lamp ought to be very small. Sudden heating 

 must be carefully avoided. On the neck of the lamp a tube is fixed, 

 which serves as a chimney. Its object is to make the flame steady, 

 and prevent its flickering. 



The drop of balsam is soon seen to oscillate ; the chloroform 

 which it contains evaporates, and after about a minute of heating 

 there remains a small solid hemisphere, whose hardness should be 

 kept below that of the balsam which secures the diatoms. If any 

 bubbles are formed, they should be removed with a needle, in such a 

 way as not to alter the regular shape of the hemisphere. 



After it is perfectly cold the slide is turned over, and on the 

 hardened drop is placed, exactly centrally, the cover-glass holding the 

 diatoms. Heat is then applied gradually, and the cover-glass (if 

 necessary, held in its place by a needle) slowly settles down and 

 finally rests flat on the slide. There is no reason to fear any altera- 

 tion in the diatoms in consequence of its weight, as the author has 

 never found any trace of disarrangement, even with the most delicate 

 diatoms. If the quantity of balsam forming the drop has been well 

 calculated it will form round the cover-glass a raised edge, very neat 

 in appearance, and dispensing with the external ring of varnish. 



The preparation is then complete : the diatoms are inclosed in a 

 real matrix of enamel which abnormal heat alone can soften. Exposed 

 to the summer sun in a closed apartment no disturbance of the 

 arrangement of the diatoms takes place. 



In the last operation bubbles often form which disfigure the pre- 

 paration. These may be avoided by introducing, with a needle, a 

 very small drop of common oil in the centre of the cover-glass. 



The process may be applied for mounting diatoms dried into dust. 

 In this case there must be spread on the cover-glass a small quantity 

 of balsam made very fluid with chloroform, in order to secure its 

 being as thin as possible, and the heating and mounting are then 

 proceeded with as above described. 



On the occasion of the paper being read, a practical demonstration 

 of the process was given, of which it is said that the " preparation was 

 perfectly successful, and was not inferior to the celebrated slides of 

 Moller, It may be said that if the process of Moller remains unknown 

 the means of rivalling him is at least discovered. The members were 

 above all struck with the great simplicity of the manipulations," 



Paper Cells. — ^Mr. G, Busk writes as follows : — 



" As I have found the use of paper cells very convenient for the 

 mounting of objects where it is advantageous to avoid compression 

 beyond a certain point (as for instance Hydroids, Polyzoa, &c.), I 



