10 INTRODUCTION. 



specimen is affected by water, as is the case with mucilagi- 

 nous tissues, crystalloids, etc. As a reagent for use under the 

 cover-glass it is more satisfactory than common alcohol, but 

 in keeping it the greatest care must be exercised to exclude 

 moisture. 



41. Alum. Either potash- or ammonia-alum may be used to 

 diminish the transparency of cells which have been acted on by 

 potassa (see 24). Alum is a mordant in some of the processes 

 for staining (see ( J8). 



42. Ammonia. Aqueous ammonia may replace the fixed 

 alkalies, potassa and soda, but possesses no advantage over 

 them except in its somewhat slower and less violent action. 

 For its use in the examination of albuminoids, see 125. Its 

 principal use in microscopy is in the preparation of certain 

 staining agents (see 77) and cuprammonia. 



43. Anilin chloride. Dissolved in alcohol, this reagent im- 

 parts a pale 3*ello\v color to lignified cell-walls. Upon addition 

 of Irydrochloric acid, the color is much deepened. This is Hohnel's 

 test for lignin. 



44. Anilin sulphate. This substance in aqueous or alcoholic 

 solution gives to lignified cell-walls a pale yellow color, which is 

 much deeper when the reagent is followed by sulphuric acid, 

 Wiesner's test for lignin. 



45. Argentic nitrate, or nitrate of silver, in extremely dilute 

 alkaline solution freshly made, has been recommended for dis- 

 criminating between living and dead protoplasm, the former 

 turning dark, the latter remaining unchanged (see details in 

 Part II.). 



46. Asparagin. A concentrated solution of asparagin is 

 suggested by Borodin for the recognition of asparagin itself 

 when its ciystals have been formed in tissues blanched by dark- 

 ness. 



47. Auric chloride, long used for staining preparations in 

 animal histology, has been somewhat employed for coloring the 

 cells of certain lower plants, and in the same manner as argentic 

 nitrate, for detecting the condition of protoplasm. 



48. J3enzol is a powerful solvent for various vegetable fats 

 and resins. It is also used for the preparation of benzol-balsam 

 (see 112), and in dissolving paraffin (see 8). 



49. Calcic chloride. Treub emplo}'s this for clearing tis- 

 sues. The fresh section, after having been moistened by a 

 little water, is covered with dry powdered chloride, warmed 

 until it is about dry, and afterwards placed in a little water. 



