18G O. P. Dellinger. 



photographs. Actinosphaerium was chosen because of its long, finely 

 drawn out pseudopods, which have a central core of fibrillae. In 

 taking the records only the fibrillae were considered. 



In all, twenty-eight different agents were tested. They represent 

 the killing fluids generally used in cytological studies. For conveni- 

 ence I have arranged them in seven groups according to some one 

 reagent they contain. Some reagents are found in more than one 

 group. 



All observations were made under a 1.5 mm. (Spencer Lens Co.) 

 Objective and No. 1 eye-piece. 



Osmic Acid Group. 



This group contains osmic acid, 4 per cent., 1 per cent, and 2 per 

 cent.; osmic acid 2 per cent., 95 per cent, alcohol, equal parts; 2 per 

 cent, osmic acid mercuric bichloride saturated in normal salt, equal 

 parts; 2 per cent, osmic acid, 10 per cent, formol, equal parts, and 

 strong and weak Flemming. (If two or more reagents enter into a 

 solution it was made up just before using. This holds for all reagents 

 in all groups.) These reagents prove to be the more satisfactory in 

 preserving cilia than those of any other group. In most cases the 

 cilia are well fixed in nearly normal condition. Strong and weak 

 Flemming are the exceptions. 



Osmic acid: — Cilia treated with osmic acid in solutions of A per 

 cent., 1 per cent, and 2 per cent, strength seem entirely normal. They 

 are full length and straight. (PI. I, Fig. 2). After making many 

 tests with the three solutions the author favors the 2 per cent, solu- 

 tion as the most reliable. 



Two per cent, osmic, 95 jier cent, alcohol : — This combination is a 

 fair killing agent. 



Two per cent, osmic -f- mercuric bichloride : — This solution next 

 to osmic acid gave the best results. Cilia treated with it are full 

 length and straight. 



vStrong and weak Flemming: — These two solutions so universally 

 used in cytological studies gave the most unsatisfactory results of any 

 in this group. Cilia are apparently broken or twisted into what ap- 

 pears to be short, crinkled threads. (PI. I, Fig. 3.) These threads 



