1884.] 



MICROSCOPICAL JOURNAL. 



211 



quently happens, with some prepar- 

 ers, that the cover-glass becomes cov- 

 ered w^ith a fihn of oily or watery 

 particles which condense upon its un- 

 der surface. This matter has already 

 been alluded to under dry mounting, 

 but Prof. W. A. Rogers, whose 

 rulings, as formerly prepared, were 

 frequently injured in appearance by 

 this condensation, has at last, so he 

 believes, entirely obviated the annoy- 

 ance. He no-sv uses a brass ring for 

 a cell to hold the ruled cover-glasses, 

 but free communication between the 

 air ^vithin and without the cell is es- 

 tablished througli a minute perfora- 

 tion in the side of the cell. Some 

 preparers have been in the habit of 

 maintaining free communication be- 

 tween the air without and within the 

 cells by leaving a bristle or a thread 

 of some kind passing through the 

 'wall of the cell until the mount is fin- 

 ished, after which it is withdrawn, 

 thus making a minute perforation. 



The writer, being absent from 

 home and unable to consult memo- 

 randa and books of reference, has 

 been unable to give the promised 

 formulas of various mounting media 

 in this article. They will be given 

 in future. There will also follow 

 some instructions for killing and 

 mounting soft and very delicate or- 

 ganisms, such as amcEbae, infusoria, 

 etc. It requires considerable skill 

 and experience to make preparations 

 of this kind that are of lasting scien- 

 tific value, but the results that can be 

 obtained are well worthy of the ex- 

 penditure of time required. 



Microscope of Large Field.* 



Of late years there has been seen in 

 the domain of technique in anatomy 

 a reform which to-day is almost com- 

 plete. For the scalpel and dissecting 

 needle have been substituted the razor 

 and microtome ; for the laborious 

 dissection of minute organisms under 

 the mounted lens the more sure 



*Note by M. A. Gravis. Translated for this Jour- 

 nal from Bull. Soc. Beige de Micr. 



method of successive sections is pre- 

 ferred. Applied first to the study of 

 objects of very minute size, the 

 method of successive sections has be- 

 come rapidly generalized, and to-day 

 it is applied with success in the re- 

 searches made on creatures of which 

 the section measures sometimes sev- 

 eral centimeters in diameter (adult 

 plants, young fishes, small reptiles, 

 etc.) 



From this it has resulted that the 

 dissecting microscope has been little 

 by little discarded and replaced by 

 the ordinary compound microscope. 

 But the latter, owing to its magnify- 

 ing power, is especially adapted to 

 the detailed histological study of the 

 organs. The small field of view, on 

 the other hand, makes it less useful 

 in the study of the relations of posi- 

 tion pi-esented by the various kinds of 

 tissue in a section of large diameter. 

 The need of a new optical instru- 

 ment begins, therefore, to be felt 

 among naturalists. 



Several months ago, finding my- 

 self at the house of M. Nachet, in 

 Paris, I spoke to that able con- 

 structor of this desideratum of ana- 

 tomical laboratories. M. Nachet im- 

 mediately showed me a microscope 

 which he had made for the purpose 

 of observing large sections with a 

 feeble magnification. If this new 

 microscope does not realize all the 

 perfection desired, it still constitutes 

 a very happy tentative device, and a 

 real progress. I believe, therefore, 

 a description of this instrument, 

 which is now in the possession of the 

 laboratory of the Botanical Institute 

 at Liege, will be of value. 



The new microscope of Nachet is 

 a compound microscope, which dif- 

 fers from those in use by some modi- 

 fications which I shall proceed to 

 mention. 



The stand is much larger than or- 

 dinary. The stage has a large open- 

 ing illuminated by a mirror of large 

 diameter. The tube, of which the 

 invariable length is 195 mm. and the 

 interior diameter 29 mm., is provided 



