428 Mr. T. Goodey. The Excystation of [Feb. 28, 



preparations. A drop of hay-infusion or other liquid medium* is taken on a 

 loop of platinum wire and spread out on a clean cover-slip ; into the liquid is 

 placed a number of cysts of Colpoda, and the cover-slip is then inverted over 

 the hollow of a cavity slide and the edges waxed down by painting round 

 with the hot wick of a candle. It is then allowed to incubate. In order to 

 experiment further with the excysted organisms, the cover-slip is carefully 

 lifted by means of a needle, and after the necessary treatment it is replaced 

 and the edge waxed down again. Where not otherwise stated incubation has 

 been carried out at 30° C, this being the temperature at which excystation 

 is most rapid. 



Material. — The investigations have been principally carried out with the 

 resting cysts of Colpoda cucidlus. A culture of this species, of a particular 

 strain measuring about 45 /a in length and having a rather pointed anterior 

 end, was obtained free from any other ciliated protozoa. By making sub- 

 cultures of this from time to time in sterile 1-per-cent. hay-infusion, and 

 allowing the Colpoda to go on multiplying and encyst, quantities of resting 

 cysts were obtained. For convenience the cysts were collected on small 

 filter papers and kept in an air-tight glass dish. A quantity of cysts of a 

 larger strain of Colpoda cucidlus was also obtained, but these did not prove to 

 be so convenient for manipulation as the smaller strain. 



It was found that if the cysts were kept for some weeks on the filter 

 paper in a quite dry condition, their power of excysting rapidly was con- 

 siderably diminished. Excystation was most rapid in the case of cultures 

 made from cysts recently filtered and almost air dried. 



Influence of Temperature on Bate of Excystation. — Hanging-drop cultures 

 were made with cysts in hay-infusion and put into incubators at different 

 temperatures, 40°, 30°, 25°, and 20° C. The cysts were all from the same 

 collection and the hay-infusion from the same stock solution, so that 

 conditions were all similar, except for temperature. 



The results were as follows : — 



40° C, none excysted after several hours. 

 30° C, many active after 1 hour incubation. 

 25° C, a few active after 1 hour 17 minutes. 

 20° C, a few active after 2 hours 12 minutes. 



It is evident that differences in temperature have a considerable influence 

 on the rate of excystation. It was not possible to determine exactly the 



* Distilled water, tap-water, and aqueous soil-extract were used at different times. 

 Excystation takes place quite freely in distilled water. 



