44 J- MCA. KATER AND R. I). BURROUGHS. 



pletely disappeared without the formation of a single cyst. A 

 little later twelve cultures were seeded and six of these were 

 placed in the laboratory, the other six at a temperature of 30 C. 

 In two days all were excellent cultures and many cysts had 

 appeared in the ones kept in the laboratory, while none had 

 encysted at 30. On the third day all were alike, fair cultures 

 with many cysts. The reason for these encysting more quickly 

 than those of Series A will be explained later. 



A second set of temperature experiments was started some 

 time after series A. Series Bi, BT, and .64 were kept at the same 

 temperatures respectively as Ai, A2 and A$. Series B2 was 

 kept at i5-22 C. With only slight variation the results were 

 the same in series B as in A. Observations were made earlier 

 than in A and it was found that the cultures kept at the lower 

 temperatures, developed much more slowly than at the higher 

 ones, such as laboratory temperature. Series Bi and B2 were 

 still in rather poor condition on the seventh day while .84 was in 

 good condition and a few cysts were present. 



As noted above, a very few cysts appeared in five of the 

 cultures of Ai. This was not true for Bi as no encystment 

 whatever occurred. The experiment was discontinued on the 

 fifty-first day and seven cultures of series Bi had completely 

 died out, the remaining five were in fair condition. These five 

 were permitted to remain in the laboratory and in five days 

 they had completely died out without any encystment. 



We see that, as a whole, no encystment occurs at extremely low 

 or high temperatures. Behavior at high temperatures differs 

 from that at low in that, in going up the scale, encystment is not 

 prevented until a point is reached which will kill the flagellates in 

 a few days, while at low temperatures they develop more slowly 

 and make very long lived and good cultures. 



How are these results to be interpreted? At low temperatures 

 one would expect the rate of metabolism to be lower and the 

 time before encystment to be longer, but when the cultures died 

 out without encystment a new light was thrown on the problem. 

 If encystment were a response to adversely low temperatures we 

 would expect it to occur there first. On the other hand, if 

 encystment were a response to adversely high temperature we 



