316 Miscellaneous. 



tion let fall upon a cold surface becomes nearly hard. The cement 

 is then ready for use. If it is afterwards found requisite to melt it 

 again, a little oil of turpentine should be added before applying the 

 heat. 



To attach the caoutchouc ring to the glass, proceed as follows : — 

 Lay the ring upon the table, and above it place the glass object-slide, 

 so that the ring occupies the centre of the slide, and a free margin of 

 glass is left around it. A pencil is now to be dipped in the warm 

 luting, and carried over the portion of the glass through which the 

 ring is seen, care being taken to spread the luting in a thin layer, as 

 the superfluous fluid would otherwise flow out from the edges. The 

 ring is now removed from beneath the slide, and laid upon the spot 

 marked out for it with the cement. The plate is next warmed by 

 holding it over fire, and then laid, ring downwards, on a cold piece of 

 mirror glass till the cement has become cool and hard. 



Gutta-Percha Cells. 



Gutta-percha, which, like caoutchouc, resists the action of almost 

 all chemical agents, has, besides, the property of becoming soft and 

 plastic in \varm water, and can thus be fashioned into any required 

 shape, which it retains on cooling and resuming its former consistence. 

 Gutta-percha sheeting may be procured in commerce, like caoutchouc 

 sheeting, of any thickness, and vnll be found very useful for micro- 

 scopical purposes. Plates of this substance may be provided of various 

 thicknesses, according to the required depth of the cells, — for example, 

 from i^th of a millimetre to three millimetres (^ jiyth to ^th of an 

 inch) in thickness. These plates must then be cut into square pieces, 

 a little narrower than the glass slides on which they are to be fastened. 

 The openings may be cut out with scissors, or struck out with a 

 punch and hammer, the plate being laid upon a piece of cork. To 

 fasten gutta-percha rings to the glass plates the cement recommended 

 for caoutchouc is employed, and the process conducted in the same 

 way, with this difference, that, after the last heating, which makes 

 the gutta-percha soft again, pressure should be made upon it for a 

 few seconds with a cold piece of mirror glass. The upper surface of 

 the cell is thus rendered quite flat and smooth, so that the glass 

 cover, when applied, is everywhere in contact with it. In this respect 

 the gutta-percha cells are preferable to those of caoutchouc, the upper 

 surface of which, especially about the edges, has always some degree 

 of convexity. — Vol. ii. pp. 125-127. — Monthly Journal of Medical 

 Science, April 1852. 



ARENARIA SERP\LLIFOLIA. 



Messrs. Hooker and Arnott observe (Br. Fl. p. 67) : "Mr.W. Wilson 

 finds a var. at Bangor with five stamens and the petals only a quarter 

 as long as the calyx, which has prominent ribs." Mr. Babington 

 copies the observation, * Manual,' 3rd edit. p. 49. 



Specimens agreeing with this description are not uncommon at this 

 season on the sandy commons of Surrey ; they appear to be only the 

 autumnal state of the common plant.— Samuel Octavtjs Gray. 



1 



