ZOOLOGY AND BOTANY, MIOKOSCOPYj ETC. 743 



I. Clakification. 



1. Generally the tissues are made transparent at the same time 

 that thin sections are prepared. For this purpose recourse is had to 

 the alkalies (ammonia or potash), to glycerin, and to chromic, acetic, 

 carbolic, and nitric acids. 



Ammonia. — Prof. Dippel * uses ammonia to give transparency 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. 



Potash. — This substance is of more general use than ammonia. It 

 especially thins cell-walls of cellulose membranes. Poulsen,f Nageli, J 

 Dippel, § Wiesner, 1 1 and Sachs ^ 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 themselves 

 or upon the organs before they are cut. In this case the alcoholic 

 solution is the best. Eussow ** has made a good preparation of it by 

 pouring into alcohol of 85 or 90 per cent, a concentrated 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. 



Hansteinfl 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 neutralize 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. 



Acetic acid. — The effect of this acid is very perceptible when care 

 is taken to wash the preparations in distilled water before submitting 

 them to its action. It assists the examination of the nuclei, which it 



* ' Das Mikroskop,' i. (1867) p. 279. 



t Loc. cit. 



t ' Das Mikroskop,' 1877, pp. 472 and 525. 



§ 'Das Mikroskop,' i. (1867) p. 278. 



Il ' Technische Mikroskopie,' 1867, passim. 



^ " Ueber die Stoffe welche das Material der Zellhaute liefern," in Priagsh. 

 Jahrh., iii. 1863. 



** Mem. Acad. St. Petersburg, six. p. 15. 



tt " Die Entwiekelung des Keimes der Monocotyl. und Dicotyl." in Hanstein's 

 Bot. Abhandl., Bonn, 1870. 



