ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 



527 



Fig. 128. 



owing to the greater loss from absorption and reflection in the glass 

 block. Owing to the increase of divergence of the pencil u^ on its 

 exit from G, the pencil which jast fills the pupil of the eye is, within 

 the glass, of a smaller angle [u^) than that 

 pencil (Wg) which reaches the eye direct from 

 air. Thus the greater intensity of radiation 

 within G is just compensated for by the 

 diminished angles of the pencils which are 

 admitted to the eye (it 1 : u^ \: 1 : n for narrow- 

 angled pencils). 



&. 



Collecting', Mounting and Examining 

 Objects, &c. 



Deby's Improved Growing-slide.* — Ee- 

 ferring to the growing-slide described at 

 p. 333 of vol. iii., Mr. Deby says that some 

 difficulty seems to have been found in the 

 making of these slides, so that he has devised 

 a still more simple contrivance for obtaining 

 the same results. Take an ordinary glass slip, 

 with a circular hole, say half an inch or more 

 in diameter, in the middle ; lay this slip on an 

 ordinary glass slide, not perforated. Then 

 grease the top of the upper or perforated slide 

 just a little way around the circular hole, and 

 join the two slips of glass by means of two rubber rings. The object 

 is then placed on a thin cover-glass, somewhat larger than the hole in 

 the slide ; it is then covered by a thin glass cover, ^ inch in diameter ; 

 the whole is then turned down and fastened to the slide by the 

 adherence of the grease while the small cover prevents the running 

 of the liquid. The plant or animal under examination finds itself 

 confined in a sort of miniature Ward's case. When not under observa- 

 tion, the growing slide is laid flat in a sl^allow plate with water just 

 above the line of junction of the two slips of glass, where, by capil- 



FiG. 129. 



larity, it creeps up to the central cell, where evaporation keeps the 

 contained atmosphere in a state of constant and healthy saturation 

 (see Fig. 129). 



Method for Colouring Infusoria and Anatomical Elements 

 during Life.t — M. A. Certes has endeavoured to find some drug which 

 would stain bodies during life ; and he finds that Infusoria placed 

 in a weak solution of chinolin or cyanin are coloured a pale blue, and 

 may continue to live for as many as thirty-six hours ; strong solutions 

 are immediately fatal. After being for twenty-four hours in a damp 



* Joum. Quek. Micr. Club, vi. (18S0) pp, 166-7. 

 t Comptes Eendus, xcii. (1881) pp. 421-6. 



2 N 2 



