On the Emploijment of Dammar in Microscopy. 35 



" Having then examined, with the various objectives which passed 

 in review under my scrutiny, the specimens I possessed mounted 

 in the two ways most commonly in use — that is to say, dry in air 

 and in Canada balsam — it struck me that it would be well to try 

 the effect of various media in assisting the performance of the 

 instrument used ; and, to that end, I mounted several specimens in 

 different ways and in various varnishes and hquids, amongst which 

 one may be particularized as very difficult to manage — that is to 

 say, benzole. Amongst all the varnishes which I tried, I obtained 

 the best results with a specimen of very old Dammar, which I was 

 lucky enough to meet with in a small quantity, and which I was 

 assured, by the person from whom I procured it, was of superior 

 quality as a varnish, on account of its having been made some time, 

 and at a period when spirits of turpentine and not petroleum 

 naphtha was used in its manufacture ; the latter material being 

 used at the present time for dissolving gums and resins in varnish 

 making, the war having rendered turpentine extremely scarce, as 

 is well known. 



" Old Dammar varnish, then, is the medium which I wish to re- 

 commend to the notice of the members of the microscopic fraternity ; 

 and as to the points in which it is superior to Canada balsam, I 

 would state that its refractive power is such that markings which 

 are with difficulty seen in balsam with a ith objective are with ease 

 brought out sharply and distinctly when mounted in the Dammar 

 with a x%ths. It also dries almost immediately and without the 

 use of much heat ; in fact, much heat is rather detrimental, and I 

 find the best method of procedure to be to dry the specimens 

 of diatoms upon either the slide or thin cover as is desired, 

 although the latter plan is the best, and shghtly warming, drop 

 upon them a very small quantity of pure spirits of tui-pentine, and, 

 before it has all evaporated but has permeated throughout the 

 mass of diatoms, to add the Dammar and bring the cover and shde, 

 both shghtly warmed, together. When mounting a number of 

 specimens (say a dozen or so), as soon as we have put the cover 

 upon the last the first is ready for cleaning, which can then be 

 done with a small bradawl so as to remove the superfluous varnish, 

 and the slide finished with turpentine. For cleaning shdes the 

 so-called " camphene " is the best material, as it is pure spirits of 

 turpentine. Another great recommendation, as I consider it, to 

 the use of Dammar for mounting microscopic objects is its great 

 toughness, never becoming brittle by age, as is well known to be 

 the case with Canada balsam. Besides, Dammar is commonly much 

 lighter in coloiu' than such Canada balsam as is generally to be 

 found in the shops. When mounting specimens containing cavities 

 — such as the Isthmise — perhaps even a httle more care is necessary 

 when using Dammar than Canada balsam; but when the effect 



