26 ACTION OF AUXETICS AND KINETICS 



If, however, the smear is first dropped on to a 

 film of 2-per-cent. agar jelly, and allowed to re- 

 main there for about an hour, the cover-glass can 

 then be lifted off quickly and dropped on to a 

 second jelly which contains the fixative. It can 

 then be removed at leisure and stained by the jelly 

 method, the cover-glass being removed from the 

 jelly and mounted in balsam when the required 

 degree of staining is obtained. To stain the cysts 

 (PI. VI.) we found the use of a highly diffusible 

 alkali (e.g. di-ethylamine) combined with a mini- 

 mum quantity of stain (Azur II.) most effective. 

 The drawback in staining bodies such as cysts, 

 which have thick envelopes, is that the latter 

 become highly coloured before the contents, which 

 are therefore obscured. With the jelly method, 

 using excess of alkali, the stain is forced in rapidly 

 before the dilute solution of stain has time to 

 saturate the wall. The main features of the stained 

 cysts are as follows : The ectocyst selects the red 

 portion of the polychrome dye and stains only 

 faintly!; the cyst contents, including the nucleus, 

 take on a blue or purple colour according to the 

 amount of alkali present in the jelly. The most 

 striking bodies are the " corpuscles chromatoides," 

 which appear at first comma-shaped but later become 

 solid-looking spheres (vide PI. VI. 6-8). The cysts 

 are acid-fast and are not decolourised even by 

 pure hydrochloric acid. With an excess of stain 

 the endocyst becomes a deep blue colour and its 

 contents cannot be recognised. 



It is better to select young cysts for staining 

 purposes, as old ones are so resistant. The nucleus 

 is usually single and concentric, but two of them 



