1913.] 



Colpoda cucullus from its Resting Cysts. 



439 



in cold or hot water, strong acids, fat solvents like alcohol and ether. It is 

 soluble in 4-per-cent. caustic soda at 30° C, and fails to give any reaction 

 with iodine and strong sulphuric acid. It is not digested by pepsin or 

 trypsin but is completely digested by diastase acting at 40° C, and is 

 sometimes slowly digested by the salivary ferment, ptyalin, also at 40° C. 



It is thus of a carbohydrate nature but differs from all other carbohydrates 

 which have been found in the protoplasm or secreted by the protoplasm 

 of protozoa. It seems to consist of a substance allied to glycogen, para- 

 glycogen and paramylum. The name Cystose is proposed for it. There is 

 evidence to show that the endocyst of Gastrostyla steinii is composed of a 

 similar substance. 



3. During the normal process of excystation the endocyst is set free by the 

 rupture of the ectocyst and the Colpoda liberates itself by the rapid digestion 

 of the endocyst by means of a powerful enzyme which it secretes. This 

 enzyme is put out of action by killing the excysting organisms with formalin or 

 osmic acid vapour, but continues to act on the endocyst when the organisms 

 are killed with toluene, ether, chloroform or carbon bisulphide vapours. It 

 can act when the medium surrounding the cyst contains 0*19 per cent, of 

 caustic soda on the one hand and 0'09 per cent, of hydrochloric acid on the 

 other, and may therefore be said to act in alkaline, neutral and acid media. 



It cannot act at 40° C, since excystation is inhibited at this temperature, 

 but it appears to act best at 30° C. In these respects it is remarkable and 

 differs strikingly from diastase, the activity of which is retained even as high 

 as 68° C, but is entirely checked in the presence of less than O04 per cent, 

 of caustic soda. A further point of difference from diastase is found in the 

 fact that the new enzyme fails to digest soluble starch. The name Cystase is 

 proposed for it. 



General Conclusions. — The endocyst membrane of Colpoda, and probably of 

 other ciliated protozoa forming double-walled resting cysts, is composed of a 

 carbohydrate which is different from all carbohydrates previously described. 

 To this substance the name " Cystose " is given. During the process of 

 excystation the endocyst is digested by a powerful enzyme secreted by the 

 enclosed Colpoda. The name " Cystase " is proposed for this ferment. 



My best thanks are due to the Lawes Agricultural Trust for allowing me 

 to carry on the work at this Laboratory. I am also indebted to various 

 members of the Laboratory staff and other friends for helpful suggestions, 

 particularly to Mr. W. A. Davis. Organic Chemist here, for suggesting the 

 names " Cystose " and " Cystase." 



