430 



Mr. T. Goodey. The Excy station of . [Feb. 28, 



at O09 per cent, only one or two, and at O'l per cent, none were active ; 

 0'1-per-cent. HC1 is then the critical strength which inhibits excystation. 

 Colpoda excystation can therefore take place within fairly wide limits in an 

 alkaline medium containing - 18 per cent, or - 19 per cent. NaOH and in the 

 presence of - 09 per cent. HC1. 



Tests for the Nature of the Ecto- and Endo-cysts. 



Fabre found that the ectocysts of resting cysts could withstand the action 

 of concentrated sulphuric acid for a long time, and also caustic potash solution. 

 He failed to obtain a cellulose reaction with iodine and sulphuric acid, whereas 

 Stein obtained a wine-red coloration in this manner with Vorticella microstoma, 

 and believed that the cyst-membranes of this organism were composed of a 

 substance combined with cellulose, which could be dissolved out by the action 

 of caustic potash. 



In the course of the present investigation the following tests have been 

 applied in order to determine the nature and characteristics of the ectocyst 

 and endocyst membranes of Colpoda cucullus. 



Solubility in Water. — Both ectocyst and endocyst are insoluble in cold 

 water and in water or 1-per-cent. hay -infusion at 95-100° C. 



Acids. — Sulphuric acid, strong, does not affect either ectocyst or endocyst 

 in the cold. Acetic acid, 90 per cent., has no action on ectocyst or endocyst 

 in the cold. Hydrochloric acid, strong and cold, causes the ectocyst to swell 

 up slightly, but does not dissolve the endocyst. On gradually heating up 

 cultures containing ectocysts and endocysts with 2-per-cent. hydrochloric 

 acid, and keeping the temperature at about 97° C. for half an hour, the 

 endocysts disappeared, whilst the ectocysts remained somewhat swollen. 



Alkalies. — Caustic soda : 1 per cent., 2 per cent., and 4 per cent, do not 

 dissolve ectocysts or endocysts in the cold, though they penetrate freely into 

 the endocysts and attack the Colpoda within, causing them to swell up and 

 become transparent. At 30° C, 1 per cent, and 2 per cent, still do not 

 attack the endocyst membrane, though 4 per cent, causes its solution at 

 this temperature. Twenty-per-cent. caustic soda, acting in the cold, causes 

 the ectocyst to swell up considerably and become transparent, though 

 there still remain indications of the layers making up this membrane. 

 Caustic potash : 1 per cent, and 2 per cent, do not dissolve ectocysts or 

 endocysts in the cold. 



Fat Solvents : Alcohol, 95 per cent., ether, toluene, and chloroform do not 

 dissolve the ectocyst or endocyst when added to a culture which has been 

 exposed to the action of osmic vapour for a few seconds in order to kill the 

 active and excysting organisms. 



