16 INTRODUCTION. 



staining agents. Hence it is impossible to lay down rules 

 wliich will appl^' to all cases in which tissues are to be stained : 

 the staining of the nucleus, however, can be readily secured by 

 following the explicit directions given in the chapter on "Cell- 

 growth." 



79. Of the whole class of staining agents, it ma}- be said that 

 exposure to strong light diminishes the brilliancy of the coloring 

 the^- produce in the specimen, and in many cases completely 

 destroj's it. In general, the staining obtained by allowing the 

 specimen to remain for a long time in a dilute solution of a 

 dye is more satisfactory than when a stronger dye is used with 

 haste. 



80. Cakmin. Two grades are readily procurable in this coun- 

 try ; namely, (1) " No. 40," (2) " Orient." The former is the 

 cheaper, and will answer for all cases described in this treatise ; 

 but attention must be called to the fact that it is sometimes 

 adulterated, and hence it may be found necessary to change the 

 proportions given in the following formulas. A good carmin, 

 even of the grade first mentioned, should leave only little residue 

 when placed in strong ammonia. If more than a trace of resi- 

 due is found, the amount of carmin in the formula must be 

 proportionately increased. 



81. Ammonia-carmin. Pure powdered carmin is rubbed 

 up with a little water to form a thin paste, enough strong am- 

 monia to dissolve it is cautiouslj' added, and the whole is then 

 filtered. The filtrate is to be evaporated slowly over a water- 

 bath. The dried mass dissolves readily in water, forming a 

 clear liquid which keeps well ; but it is better to preserve the 

 mass in a tightl3--stoppered bottle, dissolving it only as required 

 (Hartig's carmin).' 



82. A modification of this carmin is made as follows : .2 to 

 .4 gram of carmin is shaken up with 30 c. c. of water, and a 

 few drops of ammonia added. A part of the carmin dissolves, 

 and is to be filtered. If the filtrate smells strongly of ammo- 

 nia, it is allowed to stand for half a daj- under a bell-jar. A 

 drop of ammonia will re-dissolve any slight trace of carmin 

 which may separate. This fluid is to be added to water, drop 

 by drop, until the right color is obtained (Gerlach's ammonia- 

 carmin).'' 



83. If, to the filtrate last mentioned, 30 grams of glj'ceria 



1 Dippel : Das Mikroskop, i. p. 284. 



2 Behrens : Hilfsbuch, p. 257. 



