32 T-a'ciify-si.\-fIi Annual Meeting 



insect larvae will, as you know, stand almost anything in the way 

 of foul water. The rotifers do not go down into the stagnant 

 water. 



Chairman Whitaker: Over how long a period of time did 

 your observations extend? 



Professor Birge: A space of two years. 



Chairman Whitaker: I meant as to season? 



Professor Birge: I have gone right through the summer and 

 winter. I began in July, 1894, and \\'ent along from that 

 time, making more numerous experiments during the summer. 

 Taking the year through, nearly every other day, during the two 

 years. 



Mr. Tomlin: Was it not very warm weather during all this 

 time of the epidemic? 



Professoi Birge: Not extremely hot. We were not doing 

 any work on temperatures at that time, but whether the season 

 is very hot or very cold makes very little difference in the tem- 

 perature of the deep water. The temperature of the deep water 

 depends a good deal more on the concurrence of the warm 

 weather and- alternate calms and high winds in the early spring 

 than it does on anything that happens in the summer. After this 

 middle zone is established the bottom water does not get affected 

 at all l)y warm weather. 



Chairman Whitaker: Does it not later in the season? 



Professor Birge: Not until Septeni])er, and then the surface 

 water has cooled gradually before the bottom water gets affected. 

 The temperature of the bottom water rises rapidly ])efore the 

 first of June, and then keeps very nearly uniform until late 

 in September, when it goes up pretty rapidly in connection with 

 the mixing of the temperatures by the wind, as the temperature 

 on the surface of the water falls. 



Mr. Stranahan: Was this mortality confined to the portion 

 of the lake over the deep water? 



Professor liirge: That is hard to answer specific- 

 ally. These points all came to me years after the affair 

 was over, and I did not take all the ol^scrvations then that 

 I would now, but it was generally true that the dying fish were 

 out in the open lake. As I recollect it, I do not recaU seeing any 

 dying fish close to the shore, unless there was a strong wind 



