578 PROTOZOA 



COMMON FIXATIVES FOR PROTOZOA 



1130. A saturated solution of mercuric chloride (HgClg or 

 corrosive sublimate) in distilled water is contained in numerous 

 fixatives, and will be referred to below as sublimate solution. 

 Unless otherwise stated, films should be fixed for ten to thirty 

 minutes, and pieces of tissue one-half to several hours, according 

 to size. Most fixatives may be well used warm (40° to 42° C.) 

 to increase penetration, and sometimes even hot. All prepara- 

 tions so fixed require thorough washing in 70 per cent, alcohol 

 to remove the excess of mercury. This may be facilitated by 

 adding a little iodine to the alcohol used for washing until it is 

 no longer decolourised. Care must be taken to remove all iodine 

 as well as mercury before attempting to stain. This inay speedily 

 be done with sodium thiosulphate solution, but as a rule 70 per 

 cent, alcohol, changed once or twice, is all that is necessary. 

 Tissue is often washed after being cut into sections. Films and 

 tissues are all the better for being left in 90 per cent, alcohol for 

 some hours to harden, the preparations being then less likely to 

 undergo maceration or shrinkage during staining. 



1131. Sublimate-Acetic. One to five per cent, of glacial acetic 

 -acid added to the sublimate solution. 



1132. Schaudinn's Fluid {Zool. Jahrh. Abth. Anat., xiii, 1900, 

 p. 211). Two parts sublimate solution to 1 part absolute alcohol, 

 with, if desired, a trace of glacial acetic acid. 



Woodcock {Phil. Trans., ccvii, 1916, p. 379) and Wilson 

 {Univ. Calif. Pub. Zool., xvi, 1916, p. 244) recommend the addition 

 of 5 per cent, glacial acetic acid. Langeron (1913) shows that 

 the alcohol used need not be stronger than 90 per cent. 



This is a very important fixative for protozoa. It may be 

 used cold or warmed to 60° or 70° C, when it is more penetrating 

 and, therefore, requires rather less time. 



Maier's modification : distilled water, 200 c.e. ; absolute alcohol, 

 100 c.c. ; sodium chloride, 1-2 grm. ; HgCla, 10 grm. Ten minutes is 

 long enough to fix thin films, it was found by Minchin {Quart. Joum. 

 Micr. Sci., Ix, 1914, p. .502) to be excellent for fixing trypanosonies in 

 films or in the mid-guts of fleas, though not so good as Flemming's fixa- 

 tive for the tissues. He attributes this to unequal penetration, surmis- 

 ing that the alcohol diffuses into the tissues and fixes them defectively 

 before the sublimate can reach them. 



1133. Sublimate-Formol. Bouin's formula {Arch. Biol., xvii, 

 p. 211, 1900), §117. 



Carleton's formula {Hist. Technique, 1926, p. 37) — 1 part of 

 formol to 9 of sublimate solution. 



Penetrating and useful for cysts and tissues as well as for 

 free protozoa. 



1134. Sublimate-nitric. Petrunkewitsch and Gilson's mix- 

 tures (§74) may be used warm to fix spores and cysts. 



