352 SUMMARY OF CURRENT RESEARCHES RELATING TO 



Smith's Mounting Media.* — H. L. Smith describes his colourless 

 medium (1 • 8 to 2 ■ refractive index). It consists of arseuite of 

 antimony (a white powder) dissolved in liquid chloride of arsenic 

 until a somewhat dark-coloured honey-like viscid fluid is obtained, 

 which is used precisely like balsam. Caution is required in the 

 manufacture, which should bo done in small quantities and in a 

 homcDopathic vial. This should be about one-third filled with the 

 chloride and some of the arsenite, say one-third the bulk of the liquid, 

 added, and the mixture warmed over a spirit-lamp until all is dis- 

 solved ; then successive portions of the arsenite are added and 

 dissolved until the viscid fluid is obtained. If the ingredients are 

 clean, no filtering will be required. In mounting, the boiling should 

 be prolonged until the large easily-formed bubbles of the excess of 

 chloride disappear ; the portion outside will be hard, and require a 

 sharp edge to remove it, care being taken not to disturb the cover. 

 After this the cover and adjacent parts can be washed over with tissue 

 paper moistened with hydrochloric acid ; not water or alcohol, as they 

 decompose the medium, causing it to become an opaque white. A 

 wax ring is the best protection for the mount. The medium improves 

 with age, and with further experiments can, it is hoped, be made to 

 give permanent mounts by obviating the tendency to deposit crystals. 



The deep-yellow medium (2 • 4 refractive index) Prof. Smith pro- 

 nounces to be entirely permanent. Its composition he keeps a secret. 

 It is to be regretted that he should have decided to inaugurate such a 

 departure from the ordinary and very salutary scientific usage in such 

 matters. In the case of dealers this can hardly be legitimately ob- 

 jected to, but we hope that scientific workers in general will not be 

 misled by Prof. Smith's example, to make a mystery of methods and 

 processes which they have hitherto been so ready to make known for 

 the benefit of their fellow-workers. 



Balsam of Tolu as a Medium for Mounting. — Mr. F. Kitton 

 writes: " It is stated in the February number of the Journal that this 

 medium is objectionable for mounting purposes, as crystals are apt to 

 form in it sooner or later. I tried it shortly after reading Dr. Kain's 

 recommendation (early in September last), and have now over a 

 hundred prei)arations in the medium. In February I went through 

 them with some trepidation, but was gratified to find that no symptom 

 of crystallization had appeared. This I should have attributed to the 

 short time that had elapsed since the preparations had been made, had 

 it not been stated that recent preparations (made about the same time 

 as mine) were already full of crystals. I can only account for this 

 by supposing that either tolu is variable in its composition, or that my 

 method of preparing and using it prevents crystallization. Dr. Kain 

 recommends alcohol or chloroform as a solvent ; I employ benzole. 

 I remember some years ago inquiries were made as to the cause of 

 crystals sometimes occurring in preparations made with balsam or 

 dammar dissolved in chloroform. As I never found them in my 



* Proc. Amer. Soc. Micr., 7th Ann. Meeting, 1884, pp. 186-90. 



