226 EXAMINATION AND PRESERVATION MEDIA 



Samples of balsam that are acid * are frequently met with, and 

 are injurious to some stains. 



There seems to be a divergence of opinion among workers as 

 to whether xylol or benzol is the better solvent for routine balsam. 

 Dr. G. L. Alexander, for instance, writes to us that he considers 

 xylol illogical because it has two methyl side groups to undergo 

 oxidation. Mr. Muir, of the Edinburgh Pathology Laboratory, 

 ahvays uses benzol, and has never had any serious trouble rvith fading. 

 We think that workers who have experienced fading with their 

 xylol balsam should try benzol, which nuist, however, be pure 

 and free from water. 



To prevent the lid of the balsam bottle from sticking, C. M. Hector 

 (Watson's Microscope Record, No. 21, 1930), uses a balsam bottle with 

 a loose-fitting cap, places a ring of plasticine around the shoulder, and 

 pushes the cap on to it. Corks are, of course, quite useless. 



484. Seiler's Alcohol Balsam {Proc. Amer. Soc. Mic, 1881, 

 pp. 60-2 ; Joiirn. Roy. Mic. Soc. [N.S.]. ii, 1882, pp. 126-7). 

 Dissolve solid balsam in warm absolute alcohol, and filter through 

 absorbent cotton. Objects may be mounted in it direct from 

 absolute alcohol. We find it for most purposes admirable. It is 

 one of the most stable solutions known to us. Care should be taken 

 not to breathe on it, as this may cause cloudiness. 



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

 are the same as for balsam. We find xylol the best. For directions for 

 preparing solutions, by various authors, see early editions. After ample 

 experience we are convinced that not one of these solutions can be depended 

 on for jjermanent jyreservation. Sooner or later, sometimes after a few 

 weeks or days, or it may be only after months or years, granules make 

 their appearance in the mounts. (See next §.) 



486. Colophonium. A solution of pale colophonium in oil of 

 turpentine keeps well and gives very good definitions. The 

 solution should not be too thick, as it thickens with age. 



This medium dries very slowly (so that ample time is afforded 

 for arranging objects in it). In the winter a slide will take about 

 a month before it will be hard enougli to be safe with oil-immersion 

 lenses ; whereas an alcohol-balsam mount will be dry enough in 

 a couple of days. It injures alum-ha^matein stains ; as it some- 

 times develops clouds of globules it is not to be depended upon. 



Dr. S. G. Scott of Oxford used both damar and colophonium instead 

 of balsam, and very few of his preparations left after his decease are 

 good. A large number have become granular. 



Reiim (Zeit. wiss. Mik., ix, 1893, p. 387) dissolves 1 part colophonium 

 in 10 of benzene. Solutions in chloroform or xylol are also used by some, 

 see NissL in Encycl. mik. Techn., ii, p. 274. 



* There are various " neutral balsams " on sale now. We buy these 

 for valuable slides, otherwise we use benzol balsam. 



