INVERTEBRATA, CRYPTOaAMIA, MICROSCOPY, ETC. 765 



previously been immersed in osmic acid, and if the latter Las once 

 completely blackened the tissue, the oxalic acid is powerless after- 

 wards to redden it. Mixed solutions of osmic acid and oxalic acid 

 stain proportionally to the relative strength of each. The chief 

 drawback to this method is the small penetrating power of osmic 

 acid, which prevents the whole thickness of a specimen from being 

 equally stained. 



Method of examining Living Cells of Larva of Newt, see p. 692. 



Undescribed Microscopes. — We believe that the following Micro- 

 scopes have never yet been described in any English treatise or 

 journal. We propose to add from time to time the descriptions of 

 any other extant forms which present any specialty, and have not 

 hitherto been described in this country. 



Fig. 1 represents the " Microscope nouveau grand modele renverse 

 avec miroir argente " of Messrs. Nachet. 



If the eye-piece of a Microscope is removed considerably from the 

 objective, the image is of course largely increased, but to obtain the 

 full advantage, it is necessary that the eye-piece should be of increased 

 diameter. The weight of this and the long tube presents, however, a 

 practical difficulty in addition to the fact that the observer is so far 

 from the stage that it is impossible for him to manipulate properly. 



To avoid these difficulties, M. Nachet conceived the idea of the 

 Microscope represented in Fig. 1. 



A strong tripod base supports a hollow brass column, the upper 

 end of which is closed by a plate with a central hole, and to which is 

 fixed a socket in which the tube carrying the objective A is moved by 

 the milled head B forming the coarse adjustment. A fine adjustment 

 is obtained by means of a second tube moved by the milled head V. 



To the side of the column is soldered another tube (placed obliquely 

 as shown in the figure), the interior of which is in commimication 

 with that of the column by an ellij)tic opening and having the eye- 

 piece at the upper end. At the bottom of the column is placed a 

 plane mirror silvered on its upper surface, and inclined at such an 

 angle as to be perpendicular to the line bisecting the angle formed by 

 the two tubes, so that all the rays from the objective pass to the eye- 

 piece. The mirror does not appreciably deteriorate the image, the 

 loss of light being insignificant. The distance of the eye-piece from 

 the objective is 90 cm., and very large amplification can be obtained. 



The stage is supported above the objective on three supports, and 

 is supplied with movements by G and D. Above the stage is a " super- 

 stage " C (which can be turned aside from the Microscojje) for illu- 

 minating apparatus, and over that the mirror with universal movements, 

 supported on an upright rod, which can be moved round the summit 

 of the column.* 



One of these instruments (from Mr. Crisp's collection) was exhibited 

 at a recent soiree of the Quekett Microscopical Club. It was first 

 exhibited at the Vienna Exhibition. 



* Cf. Robin's ' Tnute du Microscope,' 2ud ed. (1877) p. 62. 

 VOL. II. 3 B 



