898 PROTOZOOLOGY 



Distilled or tap water 200 cc. 

 10% anhydrous sodium 



bisulphite 10 cc. 



HC1 solution (a) 10 cc. 



Feulgen's reaction is used to detect thymonucleic acid, a constitu- 

 ent of chromatin. By a partial hydrolysis, certain purin-bodies in the 

 acid are split into aldehydes which show a sharp Schiff's reaction 

 upon coming in contact with fuchsin-sodium bisulphite. Thus this 

 is a reaction, and not a staining method. Smears fixed in sublimate- 

 acetic or Schaudinn's fluid are brought down to running water, after 

 being placed for about 24 hours in 95% alcohol. Immerse them in 

 cold HC1 for one minute, then place them in HC1 kept at 60°C. (over 

 a microburner or in an incubator) for 5 minutes, quickly immerse in 

 cold HC1. After rapidly rinsing in distilled water, place the smears 

 in solution (b) for 30-minutes to 3 hours. There is no overstaining. 

 The smears are then washed in three changes (at least 2 minutes in 

 each) of solution (c). Wash them in running water for 30 minutes. If 

 counterstaining is desired, dip in 0.1% light green solution and rinse 

 again in water. The smears are now dehydrated through a series of 

 alcohol in the usual manner and mounted in Canada balsam (Feul- 

 gen and Rossenbeck, 1924; Feulgen-Brauns, 1924; Feulgen, 1926; 

 Coleman, 1938; Stowell, 1945). 



Silver-impregnation methods. Since Klein (1926) applied silver 

 nitrate in demonstrating the silver-line system of ciliates, various 

 modifications have been proposed. 



Dry silver method (Klein, 1926). Air-dried cover glass smears are 

 placed for 6-8 minutes in a 2 per cent solution of silver nitrate and 

 thoroughly washed. The smears are exposed to sunlight for 2-8 hours 

 in distilled water in a white porcelain dish, with occasional control 

 under the microscope. The smears are then washed thoroughly and 

 air-dried; finally mounted in Canada balsam. 



Wet silver method (modified after Gelei and Horvath, 1931). The 

 ciliates are fixed in a centrifuge tube for 5-10 minutes in sublimate- 

 formaldehyde solution, composed of saturated corrosive sublimate 

 95 cc. and formaldehyde 5 cc. The specimens are now washed twice 

 in nonchlorinated water and once in distilled water; they are then 

 treated in 1.5-2 per cent solution of silver nitrate for 5-20 minutes. 

 Without washing, the specimens in the tube are exposed to direct 

 sunlight for 10-60 minutes in distilled water, after which the speci- 

 mens are washed 4-6 times in distilled water, one minute each. Pass- 

 ing through a gradually ascending alcohol series and xylol, the speci- 

 mens are mounted in Canada balsam. 



