434 



Mr. T. Goodey. The Excystation of 



[Feb. 28, 



process of endocyst-digestion continues. On the other hand, formalin and 

 osmic acid vapour kill the organism and also the secreted enzyme, hence the 

 digestion of the endocyst is stopped. 



After the organism has been killed by a volatile antiseptic the further 

 digestion of the endocyst is not so rapid as when the organism is actively 

 swimming about within, but this may be due to the fact that normally an 

 excysting Colpoda has a considerable mechanical effect upon the thin endocyst 

 wall as it swims about, no doubt aiding in its more rapid destruction. 



Tests on Soluble Starch. — In order to test the effect of the enzyme secreted 

 by Colpoda on soluble starch an agar medium was made in the following- 

 proportions— i-100 c.c. 0'05-per-cent. solution of soluble starch, agar-agar 

 0*8 grm. Two sterile Petri dishes were poured with this medium, and each 

 was inoculated with cysts of Colpoda which had been well teased out in 

 sterile distilled water. There were ten or twelve areas of inoculation on each 

 plate, each about 3 mm. in diameter. 



After incubating at 30° C. for an hour and a quarter, active and excysting 

 Colpoda were found on many of the inoculated areas. One or two Colpoda 

 were seen to emerge from their digested endocysts, and at these spots traces 

 of iodine in potassium iodide solution were added. A uniform blue coloration 

 resulted over the whole of the region ; there were no clear uncoloured zones 

 in the region of the digested endocysts. As controls, traces of the iodine 

 in potassium iodide solution were added in close proximity to the inoculated 

 areas. These gave exactly the same tone of blue as in the areas where 

 Colpoda had excysted. 



It is evident therefore that the enzyme secreted by Colpoda during 

 excystation is not capable of digesting soluble starch. 



Tests for the Digestibility of the Endocyst by Different Ferments. — Having 

 determined that the endocyst is digested by enzymic activity, it was deemed 

 advisable to test the digestive powers of pepsin and trypsin upon it. 

 Hanging-drop cultures were made in the usual way with resting cysts and 

 the excysting organisms were killed at the proper moment with osmic acid 

 vapour. Two or three cultures were then supplied with a platinum loop or 

 two of 0-04-per-cent. pepsin in 0'2-per-cent. hydrochloric acid,* and two or 

 three supplied with an equal quantity of - 04-per-cent. trypsin in - 5-per- 

 cent. caustic soda solution. All the cultures were then waxed down again 

 and put into the incubator at 40° C. 



Examinations were made at different times to ascertain the effect of the 



* The pepsin and trypsin were made at this strength according to the instructions in 

 Hoppe-Seyler's 'Handbuch der Physiol, und Pathol. Chemisch. Analyse,' 7th Edit., 

 1903. 



