322 THE MICROSCOPICAL NEWS, 
Ammonia. — Professor Dippel * uses ammonia to give trans- 
parency to delicate sections of plants. whose tissues would be 
lacerated by too long immersion in concentrated alkali. The 
ammoniacal gas, being rapidly disengaged in the open air, the 
action which it exercises on the tissues in an evaporating dish is 
weakened in proportion to the thinness of the sections. 
fotash.—This substance is of more general use than ammonia. 
It especially thins cell-walls of cellulose membranes. Poulsen, + 
Nageli,{ Dippel,§ Wiesner,|| and Sachs{1 have tried it in very 
different researches, and are unanimous in recommending its use 
for thinning the cell-walls, and making them clearer. 
In a weak solution it also renders protoplasm transparent. 
It is dissolved in water or alcohol. 
The solution is made to act either on the preparations them- 
selves or upon the organs before they are cut. In this case the 
alcoholic solution is the best. Russow** has made a good pre- 
paration of it by pouring into alcohol of 85 or go per cent. a con- 
centrated aqueous solution of potash in such quantity that after 
twenty-four hours there will be a deposit at the bottom of the 
vessel. It is then sufficient to decant the liquor to obtain it in 
the requisite condition. 
Hansteint+ has made use of it to study the root-cap and the 
embryo. Sections of stems, leaves, or roots immersed in it 
acquire great distinctness. Hanstein leaves them in it for several 
hours, then washes them in very dilute hydrochloric acid or weak 
acetic acid, so as to neutralise the alkali. Sometimes the latter 
treatment darkens the cells; the preparations are then exposed to 
the action of ammonia, and washed in distilled water before 
placing them in glycerin, which further clears them. 
Glycerin.—This liquid only clears thin objects preserved in it 
after a considerable time. This property is strengthened by the 
addition of acetic acid to the glycerin. 
(Zo be continued. ) 
* © Das Mikrosop,’ i. (1867) p. 279. 
‘1 Weoc: cit. 
t ‘Das Mikrosop,” 1877, p. 472 and 525. 
§ ‘Das Mikrosop,” i. (1867) p. 278. 
| ‘Tenische Mikroskopie,” 1867, passim, 
“I “‘ Ueber die Stoffe welche das Material der Zellhaute liefern,” in Pringsh. 
Jahrb., iii. 1863. 
** Mém. Acad. St. Petersburg, xix. p. 15. 
+t “ Die Entwickelung des Keimes der Monocotyl. und Dicotyl.” in Han- 
stein's Bot. Abhandl., Bonn, 1870. 
