ZOOLOGY AND BOTANY, MICKOSCOPY, ETC, 985 



in this case tlioy must bo previously passed through distilled water, 

 and placed on the glass while still wet with the solution of glue ; to 

 avoid distortion of the tissues, evaporation must only be allowed 

 until desiccation begins ; then treat with strong alcohol, which pre- 

 cipitating the glue, produces perfect adherence between the sections 

 and the glass. 



A very simple method described by Dr. Flogel also deserves to be 

 known, as it may be useful for arranging sections of objects imbedded 

 in paraffin. The process is as follows: — 5 gr. of gum arable are 

 dissolved in 100 gr. of water ; this solution is poured over the entire 

 surface of a perfectly clean glass slide, and the excess of liquid run 

 off by holding the slide vertically. 



The operation may then be conducted in two ways. 



(1) The sections are arranged upon a perfectly dry surface ; then 

 by breathing upon it, the thin layer of gum is dissolved and the 

 sections sink into it ; it is again allowed to dry, which takes place 

 rapidly. The paraffin is removed by benzol, and the cover-glass 

 coated with balsam is put on as previously described. 



(2) The sections are arranged on the wet slide to which they 

 adhere as the water evajiorates ; the desiccation being complete they 

 are finished as in the previous case. 



For thin and delicate sections the first method is preferable. For 

 sections of considerable size and thickness, the second should be 

 employed. 



Balsam of Tolu for Mounting.* — C. H. Kain recommends 

 balsam of tolu for mounting, as having a higher index than styrax. 

 It has some colour, but for such purposes as mounting diatoms, where 

 only a thin layer of the medium is required, the slight discoloration 

 will not prove very objectionable. It is perhajis possible to bleach 

 the solution somewhat. To prepare the tolu for use it should be 

 dissolved in either alcohol or chloroform (the latter is preferable for 

 many reasons) and then well filtered. It will not dissolve in benzole. 

 By a gentle heat the solvent can thon be evaporated so as to leave 

 the solution in any desired state of concentration. 



The ordinary gum benzoin (or benjamin) is quite as good as 

 styrax, if not better, but neither is so good as tolu. The gum benzoin 

 should be prepared as directed for tolu. 



Biniodide of Mercury and Iodide of Potassium and Phosphorus 

 for Mounting-t — Mr. Kain also drops "a word or two of caution in 

 regard to the use of the solution of biniodide of mercury and iodide 

 of potassium as a mounting medium. On account of its great density 

 and high refractive index it is valuable for many purposes, but 

 immersion objectives should be used on such mounts with great 

 caution. Even after the glass cover has been apparently thoroughly 

 washed, enough of the mercurial solution often adheres to cause quite 

 a deposit of mercury to accumulate on the front brasswork of the 



* Micr. Bulletin, i. (1884) p. 3G, 

 t Ibid., pp. 3G-7. 

 fier. 2.— Vol. IV. 3 T 



