CH. VIL] PREPARATION OF REAGENTS. 179 



acetic acid (No. 8) icocc, water ioocc, 95% alcohol 100 cc. , glycerin 15 to 30 cc 

 Crush the glue and put it into a bottle with the acid, and set in a warm place, and 

 shake occasionally. After three or more days add the other ingredients. This so- 

 lution is excellent for fastening paper to glass, wood or paper. The brush must be 

 mounted in a quill or wooden handle. For labels, it is best to use linen paper of 

 moderate thickness. This should be coated with the liquid gelatin and allowed to 

 dry. The labels may be cut of any desired size and attached by simply moistening 

 them, as in using postage stamps 



Very excellent blank labels are now furnished by dealers in microscopical sup- 

 plies, so that it is unnecessary to prepare them one's self, except for special pur- 

 poses. 



\ 312. Nitric Acid Dissociator. — This is prepared by mixing 80 cc. of water with 

 20 cc. of strong nitric acid. It is used mostly in dissolving the connective tissue of 

 muscle and thus making it possible to separate the fibers. Alum water is used as a 

 restrainer ^299 and 249). (Gage, Proc. Amer. Micr. Soc, Vol. XI, (1889), pp. 



34-45)- 



\ 313. Normal Salt Solution or Saline Solution. — Pure water from its differing 



density from the natural lymph acts injuriously on the tissues. The addition of a 



little table salt, however, prevents this deleterious action, or greatly lessens it, 



hence the name of normal salt solution. It is a T 6 S % solution of table salt (sodium 



chlorid) in water ; water 1000 cc, salt 6 grams, or water 100 cc, salt T R „ gram. 



\ 314. Paraffin. — Paraffin is of various melting points, hence at the ordinary tem- 

 perature of a laboratory, that melting at the lowest temperature will be moderately 

 soft, hence soft paraffin, while that melting at a higher temperature will be hard. 

 For the best results one has to mix hard and soft paraffins. Usually a mixture of 

 9 parts hard and 1 part soft paraffin will give good results, and may be called im- 

 bedding paraffin. For chloroform paraffin, 4 parts of imbedding paraffin are mixed 

 with one part of chloroform (£ 301, 272). 



\ 315. Picric-Alcohol. — This is an excellent hardener and fixer for almost all 

 tissues and organs. It is composed of 500 cc. of water aud 500 cc of 95% alcohol, 

 to which 2 grams of picric acid have been added. (It is a \% solution of picric 

 acid in 50% alcohol). It acts quickly, in from one to three days. (§ 252, 269). 

 (Proc. Amer. Micr. Soc, Vol. XII (1890), pp. 120-122). 



# 316. Shellac Cement. — Shellac cement for sealing preparations and for mak- 

 ing shallow cells (§ 233) is prepared by adding scale or bleached shellac to 95% 

 alcohol. The bottle should be filled about half full of the solid shellac then 

 enough 95% alcohol added to fill the bottle nearly full. The bottle is shaken oc- 

 casionally and then allowed to stand until a clear stratum of liquid appears on the 

 top. This clear, supernatant liquid is then filtered through absorbent cotton, using 

 a paper funnel (? 300, note), into an open dish or a wide-mouth bottle. To every 

 50 cc. of this filtered shellac, 5 cc of castor oil and 5 cc of Venetian turpentine are 

 added to render the shellac less brittle. The filtered shellac will be too thin, and 

 must be allowed to evaporate till it is of the consistency of thin syrup. It is then 

 put into a capped bottle, aud for use, into a small spirit lamp (Fig. 134). In case 

 the cement gets too thick add a small amount of 95% alcohol or some thin shellac. 

 The solution of shellac almost always remains muddy, and in most cases it takes a 

 very long time for the flocculent substance to settle. One can very quickly obtain a 

 clear solution as follows : When the shellac has had time to thoroughly dissolve, 

 i. e., in a week or two in a warm place, or in less time if the bottle is frequently 



