CANADA BALSAM. 249 



As to the old dispute about the respective merits of damar 

 and balsam, the case appears, after all, to lie in a nutshell. 

 Damar gives the better definition of delicate detail ; balsam 

 has greater clearing action, and affords perhaps more solid 

 mounts. 



It may be remarked here that for some of the purposes for 

 which these media are employed, Oil of Cedar may be founcl 

 preferable. The mounts need not be closed (except for im- 

 mersion work), as the oil soon sets hard enough to keep the 

 cover in place. 



418. Canada Balsam. Prepare with the solid balsam as 

 above described. The usual menstrua are xylol, benzol, 

 chloroform, and turpentine. Dissolve the solid balsam in one 

 of these to the required consistence. The turpentine solution 

 is to be preferred only in cases where it is desired to have a 

 medium that sets very slowly, or in view of the better pre- 

 servation of certain stains. For most other purposes the xylol 

 solution is the best. If time be an object, a benzol solution 

 should be preferred, as it sets much quicker than the xylol 

 solution. 



HEYS states that if the chloroform solution be poured into 

 long, thin, half-ounce phials, corked up, and set aside for at 

 least a month, the medium will be clearer and set much 

 quicker than if the balsam is mixed with the chloroform at 

 the time it is required for use (Trans. Mic. Soc., Jan., 1865, 

 p. 19; BEALE, p. 51). 



SAHLI (Zeit. f. wiss. Mik., 1885, p. 5) recommends oil of 

 cedar as a menstruum. 



419. Seller's Alcohol Balsam (Ptoc. Amer. Soc. Mic., 1881, pp. 60-2; 

 Journ. Roy. Mik. Soc. [N.S.], ii, 1882, pp. 126-7)." 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 and filter through absorbent cotton." 



The advantage of this medium is stated to be that objects may be mounted 

 in it direct from absolute alcohol, without previous treatment with an essen- 

 tial oil or or other clearing agent; Seiler considers that by this means 

 " shrivelling is avoided, as well as the solution of fat in the cells." 



The process is not very easy to carry out, and I cannot recommend it for 

 general work. 



420. Damar (Gum Damar, or Dammar, or d'Ammar). The 

 menstrua are the same as for balsam, and the solution should 



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