SEVENTH ANNUAL MEETING 51 



ment had been raised as little as 2° C. above that of the con- 

 trol. With the gradual rise in the temperature of the experi- 

 mental pan, the activities of the experimental fish became more 

 and more marked until in a number of instances the fish at- 

 tempted to leap out of the pan at a temperature still 2°-3° C. 

 below the maximum for the species. At this point the swim- 

 ming movements were still in perfect correlation, but, as the 

 temperature approached the maximum for the species, lack of 

 correlation began to develop and at a temperature of 1° C. or 

 less, below the maximum, a sudden paroxysm set in. The fish 

 "scooted" blindly about the pan, sometimes shooting over the 

 edge. This intense activity lasted for about 30 seconds or 

 less, when the fish fell to its side, making no visible movements 

 other than feeble twitchings of the gills and fins. If at this point 

 it was immediately removed and placed in cooler water it often 

 recovered; the possibility of recovery varied with the species 

 and size of the fish, the more hardy species (bull-head) and 

 the larger individuals of the other species (cyprinids) being 

 most likely to live. The paroxysm induced by temperature 

 resembled so much that produced in other experiments (Wells 

 '13) by lack of oxygen and excess carbon dioxide, that analyses 

 were made to determine the amount of these gases present 

 during the experiments. These analyses always showed a nor- 

 mal amount of oxygen to be present while the amount of car- 

 bon dioxide was if anything a little less than that of the con- 

 trol, the diminution being due to the higher temperature of 

 the experiment. 



In the attempt to determine a definite maximum temper- 

 ature for the different species used it was found that a number 

 of factors must be considered. The species used all resisted 

 higher temperatures when the heating was gradual, than 

 they did when it was comparatively rapid, thus showing some 

 acclimatization to the higher temperatures. Large fishes of 

 a given species were usually considered more resistant than 

 were small ones of the same species. The physiological condi- 

 tion of the species was found to be important; it has been 

 found that practically all the species of fishes occurring in the 

 rivers and creeks in the vicinity of Chicago are a great deal 

 more resistant to many kinds of stimuli, temperature included, 

 in March and April, just before the breeding season begins, 

 than they are in the latter part of June and first part of July, 

 immediately following the breeding season. In fact resistance is 

 so low at this latter time of year, that most of the species of 

 cyprinid minnows cannot be transported into the laboratory 

 from creeks an hour's ride out. even though ice be taken along 



