ZOOLOGY AND BOTANY, MICEOSCOPY, ETC. 127 



media, whereby the disadvantages attendant upon the use of balsam 

 are removed, so that it becomes the preferable method. 



Take a clear sample of Canada balsam and evaporate it in a water 

 or sand bath to dryness ; i. e. until it becomes brittle and resinous 

 when cold. Dissolve this while warm in warm absolute alcohol 

 (Squibbs'), and filter through absorbent cotton. Place the section, 

 after it has been stained, in weak alcohol (about • 60), and allow it 

 to remain in a few minutes, then transfer it to '80, "95, and finally 

 to absolute alcohol, in which it should remain a few minutes also. 

 Then transfer it to the slide (which has been slightly warmed above 

 a spirit-lamp so as to remove all moisture), drain off all superfluous 

 alcohol, and place a drop of the alcoholic balsam solution on the 

 specimen. In a few seconds the latter will become transparent, when 

 it may be covered, and set aside to dry. In damp weather, or when 

 breathed upon, a milky edge will be noticed on the drop of balsam, 

 which is caused by minute globules of water, which, however, may 

 readily be dispelled by the application of a little heat to the under 

 side of the slide. It will be seen that by the gradual dehydration of 

 the specimen, the danger of distortion of the histological elements 

 is materially diminished ; that by the omission of any clearing agent 

 the shrivelling is avoided as well as the solution of fat in the cells 

 prevented, for cold alcohol alone will not dissolve fat ; and finally by 

 evaporating the balsam to dryness all other constituents except the 

 pure balsam are driven off, so that the danger of crystallization is 

 avoided. 



Mounting in Glycerine.* — Dr. S. E. Holdsworth finds the follow- 

 ing plan to be efficacious in avoiding the difficulty found in getting rid 

 of the surplus glycerine when it has passed beyond the cover-glass. 

 He puts a very small drop of glycerine upon the object, just sufficient 

 that when the cover-glass is applied it will not extend to the margin. 

 A solution of Canada balsam in chloroform or benzoline is then run 

 in to fix the cover-glass, and not being miscible with the glycerine, an 

 air-space is formed between the two fluids which has not been found to 

 be detrimental. The slide can be finished with a ring of balsam or 

 other cement. 



Smith's Slides.f — The Editor of the ' American Monthly Micro- 

 scopical Journal ' writes : — " Mr. J. Lees Smith, of this city, has 

 prepared some very attractive slides in this manner : the glass slips 

 are first coated with photographer's ' granite varnish ' by flowing, just 

 as a plate is coated with collodion in photography. This coating of 

 varnish gives the slide the appearance of finely ground glass. It is 

 then placed on the turntable, and, by means of a knife-blade, the 

 varnish is entii-ely removed from a circular spot in the centre, just 

 large enough for the cell in which the mount is to be preserved. 

 The preparations we saw were mounted in glycerine, and the clear 

 and transparent cells were made of Brown's rubber cement, which Mr. 

 Smith regards as a most excellent cement, especially for glycerine 



* Ann. Eep. Postal Micr. Soc, 1881, p. 11. 

 t Amer. Mon. Micr. Journ., ii. (1881) p. 179. 



