1062 SUMMAEY OF CURRENT RESEARCHES RELATING TO 



by the addition of nut or poppy oil. The refractive index of this gum the 

 author has not accurately determined ; but it is so nearly identical with that 

 of crown glass that a bit of the latter substance dropped therein is visible 

 only with the closest scrutiny. 



Xylol-Daminar,* — In an article on resinous substances and the pre- 

 servation of microscopical preparations, Dr. G. Martinotti advocates the use 

 of dammar as the fittest medium for mounting microscopical preparations 

 when the general structure is desired to be brought out. In this respect 

 it is superior to Canada balsam which is most suited for throwing 

 into relief certain parts of a specimen which are deeply stained, such as 

 nuclei, micro-organisms, &c. A suitable solvent for dammar has long 

 been a desideratum, for though Flemming and Pfitzner have produced 

 dammar solutions with turpentine and benzin, the resulting fluids have the 

 fatal fault of losing their transparency in a comparatively short space of 

 time. After numerous experiments, the author finally selected xylol as 

 the solvent, and he found it to possess the necessary qualifications. The 

 medium he produced, xylol-turpentine-dammar, is a white or sKghtly 

 yellowish fluid which does not affect the anilin stains nor dissolve celloidin, 

 retains its transparency (for nine months at least), and gives a perfect 

 definition of the histological elements. Finely powdered dammar resin 

 and xylol are placed together in a closed vessel, and after some days the 

 clear supernatant fluid decanted off, or the mixture filtered. The clear 

 white fluid is then evaporated in a water-bath to a semi-fluid mass, which 

 is yellowish and resembles Canada balsam. If desired, the mass may be 

 further concentrated, and in this denser condition it does not lose its trans- 

 parency or viscidity. In practice, however, it is not necessary to proceed 

 further than the semi-fluid condition. To produce a medium suitable for 

 microscopical purposes, oil of turpentine is added. By this addition the 

 microscopical images are rendered more effective than with the simple 

 xylol solution ; the medium is less brittle when dry, and also loses most of 

 its yellow colour. The author regrets this slight defect, and thinks it 

 might be obviated if the concentration were carried out in vacuo and not 

 by the aid of heat. In a note the author appends the exact quantities for 

 making the solution. 40 gr. of powdered dammar resin, and 40 gr. of 

 xylol are left for three to four days at the ordinary temperature in a closed 

 vessel and then filtered. The filtrate is evaporated in a water-bath down 

 to about 45 gr., and to this 25 gr. (or even more) of essence of turpentine 

 are added. 



The author next refers to some solvents of Canada balsam, chloroform, 

 turpentine, benzin, oil of cedar, and xylol. Chloroform is objected to on 

 account of the yellowness which increases with time. Turpentine decolor- 

 izes certain dyes, e. g. hsematoxylin, and after a certain period bubbles of gas 

 are developed within the preparation. Benzoin is fairly good, but the 

 fluid is rather viscid. Of cedar oil as a solvent the author has no personal 

 acquaintance. Xylol gives fair results, but the colour of balsam dissolved 

 therein is markedly yellow. Safranin and other dyes seem to be injuriously 

 affected by this reagent, which moreover is destructive of certain delicate 

 structures, such as karyokinetic figures. 



Oil of lavender produces with Canada balsam an almost colourless fluid ; 

 preparations mounted therein are said to be quite elegant, especially those 

 stained with logwood. Some anilin stains, e. g. safranin, are however 

 dissolved by the action of lavender oil, but others retain their brilliancy. 

 The author, however, admits that his experience of this solvent is too short 



* Zeitschr. f. Wiss. Mikr., iv. (1887) pp. 153-9. 



