CH. VII] PREPARATION OF REAGENTS. 175 



REAGENTS FOR FIXING, MOUNTING, ETC. 



\ 297. Albumen Fixative y Mayer's). — This consists of equal parts of well-beaten 

 white of egg and glycerin. To each 50 cc. of this 1 gram of salicylate of soda 

 is added to prevent putrefactive changes. Probably a itnall amount of formal- 

 dehyde, say 1 cc. of the 40%, to 50 or 100 cc. of the fixative would suffice ; if too 

 strong the albumen would be precipitated. For method of use see \ 275. 



\ 298. Alcohol (Ethylic) — Ethyl alcohol is mostly used for histological pur- 

 poses. (A) Absolute alcohol (i. e. alcohol of 99-100%) is recommended for many 

 purposes, but if plenty of 95% alcohol is used it answers every purpose in histology. 



(B) S2% alcohol made by mixing 5 parts of 95% alcohol with 1 part of water. 



(C) 67% alcohol made by mixing 2 parts of 95% alcohol with r part of water. 



\ 299. Alum Solution. — For muscle dissociated in nitric acid (? 249) a saturated 

 solution (i. e. a solution in which the water holds all the a'uin it can. If one adds 

 an excess so that there will always be some undissolved alum in the vessel he can 

 be sure the solution is saturated after it has stood a few days. An easy way to get 

 a saturated solution is to take 500 cc. of water and add 100 grams of alum and heat 

 the water in an agate dish. All the alum will be melted, but on cooling a part 

 will crystallize out, leavinga cold saturated solution ). The saturated solution may 

 be used but, if a half saturated solution is employed, it will answer all the pur- 

 poses. For a half saturated solution take 100 cc. of water and ico cc. of saturated 

 alum water and mix the two. 



\ 300 Balsam, Canada Balsam, Balsam of Fir; Xylene Balsam. — This is one 

 of the oldest and most satisfactory of the resinous mediatised for mounting micro- 

 scopical preparations. Sometimes it is used in the natural state, but experience 

 has shown that it is better to get rid of the natural volatile constituents. A con- 

 siderable quantity, half a liter or more, of the natural balsam is poured into sha-1 

 low plates in layers about 1 or 2 centimeters thick, then the plates are put in a 

 warm, dry place, on the back of a stove or on a steam radiator, and allowed to re- 

 main until the balsam may be powdered when it is cold. This requires a long 

 time, the time depending on the temperature and the thickness of the layer of 

 balsam. By heating the natural balsam in a tin or agate vessel over a Bunsen 

 burner or an alcohol lamp the time may be greatly abbreviated. The heat should 

 not be sufficient to boil the balsam, however. 



When the volatile products have evaporated, the balsam is broken into small 

 pieces or powdered in a mortar and mixed with about an equal volume of xylene, 

 turpentine or chloroform. It will dissolve in these, and then should be filtered 

 through absorbent cotton or a filter paper, using a paper funnel.* The balsam is 

 too thin in this condition for mounting, but so made for the sake of filtering it. 

 After it is filtered it is evaporated slowly in an open dish or a wide-mouth bottle or 

 jar till it is of a syrupy consistency at the ordinary temperature. It is then poured 

 into a bottle with a glass cap like a spirit lamp. For use it is put into a small 

 spirit lamp (Fig. 137). 



*For filtering balsam and all resinous and gummy materials, the writer has 

 found a paper funnel the most satisfactory. It can be used once and then thrown 

 away. Such a funnel may be very easily made by rolling a sheet of thick writing 

 paper in the form of a cone and cementing the paper where it overlaps, or wind- 

 ing a string several times around the lower part. Such a funnel is best used in one 

 of the rings for holding funnels. 



