ZOOLOGY AND BOTANY, MIOROSOOPY, ETC. 855 



perfectly safe. If, however, the cement should tend to run in when the 

 cover is applied, the finishing coat must be delayed for a few hours. 



Mounting in Fluids,* — Mr. E. Ward writes on this subject as follows : — 

 " There are some microscopic objects that we cannot mount, either dry or in 

 balsam, nor yet in glycerin jelly, because the heat necessary to liquefy the 

 jelly destroys the structure of the object. In such cases we must use fluid, 

 but to seal up the fluid permanently is one of the difiiculties of micro- 

 mounting. I have been most successful in the way I purpose to show to-night. 

 I first make a cell of brown cement, and allow it to harden thoroughly. 

 I then spin a second ring of cement when just upon the point of mounting 

 any suitable object; then fill the cell with water or other fluid, and 

 arrange in it the object : place the cover-glass gently down, and fix with 

 a clip just strong enough to hold it in position without causing any 

 convexity, and absorb the exuded moisture by means of blotting-paper. 

 After the clip has remained for an hour or so it may be removed, and 

 another ring of brown cement spun over the junction of cell, slip, and 

 cover-glass. This will make all secure. Brown cement is not suitable if 

 used by itself for any fluids containing alcohol, because the spirit has some 

 action upon this medium. In this case the cell, after being made in brown 

 cement, should be covered entirely with balsam and benzole, and when dry 

 this is again made tacky by a thin line of balsam, which fastens down the 

 cover-glass. A ring of brown cement may be spun over all, and completely 

 seal the mount, which may be afterwards finished in any way desired." 



Media for mounting very perishable Artificial Crystal Sections.t — 

 By very perishable crystals Prof. C. Johnston means such as lose their 

 polish or become opaque in Canada balsam as well as in air. Examples of 

 these are potassium and sodium tartrate, potassium nitrate, ammonia- 

 sodium tartrate, and potassium and ammonia-sodium tartrate. Plumbic 

 acetate is especially prone to undergo decomposition. A mounting medium 

 should be transparent, and if possible colourless, enduring as such ; of an 

 index of refraction having reference to the substance treated ; free from 

 moisture, and not a solvent of the matters it is employed to defend. The 

 author mentions the following as especially worthy of attention. 



(1) Finest gum copal dissolved in chemically pure amylic alcohol. (2) 

 Finest gum copal dissolved in chemically pure absolute alcohol. (3) Dammar 

 resin dissolved in rectified spirits of turpentine. In making these solutions 

 no heat is to be used. The gum copal should be broken up to the size of 

 buckshot, set in a warm dry place for a while, and then having been placed 

 in a well dried bottle to the extent of two-thirds its capacity, alcohol is 

 poured in until the bottle seems half full. The bottle is then corked and 

 the solution is left to time. The resultant fluids should be very thick. 

 The absolute alcohol solution is highly transparent, the amylic slightly 

 opalescent. The dammar solution is made in an analogous manner. (4) 

 Dammar resin dissolved in well boiled copaiba balsam. To this latter, 

 number 3 dammar solution is added, and melted by heat until the 

 solution becomes very thick. On cooling it thins and is ready for use. It 

 is of a dark sherry colour but quite transparent, and a preservative of 

 crystalline films as ethel ether of gallic acid. (5) Boiled Chian turpentine 

 dissolved in boiled balsam of copaiba. The turpentine is boiled until, 

 when cold, it becomes nearly hard. The boiled copaiba and the turpentine 

 are then melted together, until the mass, when cold, is too thick to flow. 



* Trans, and Ann. Rep. Manchester Micr. Soc, 1886, p. 69. 

 t Johns-Hopkins Univ. Circ, vi. (1887) pp. 79-80. 



