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BULLETIN OF THE BUREAU OF FISHERIES 



temperature at which the tadpoles went into heat rigor. They found that indi- 

 viduals reared at 15° C. went into rigor at 40.3°, while for those that had been kept 

 at 25° C. for 28 days the limit of tolerance was 2.3° higher. The increased resistance 

 was only partly lost in 17 days at 15° C. Loeb and Wasteneys (1912) tested the 

 duration of survival at high temperatures of Fundulus that had been kept at 10° 

 and 27° C. Individuals that had been kept at 10° C. died in four hours at 25° C, 

 while 30 hours' exposure to 27° C. enabled the fishes to survive indefinitely at 35° C. 

 By short exposures on successive days to temperatures that normally would have 

 killed the fishes the tolerance limit was raised to 39° C, and the added resistance 

 was not wholly lost in several weeks at a temperature near the freezing point. 



A few suggestions have been made regarding the nature of the changes involved 

 in acclimatization. Davenport, in 1897, suggested that increase in tolerance might 

 be caused by a lowering of the water content of protoplasm, with consequent raising 

 of the temperature necessary to cause coagulation. Loeb and Wasteneys (1912) 

 compare acclimatization with the annealing of glass, while Miss Behre (1918) has 

 presented evidence indicating that an adjustment in metabolic rate is an important 

 factor in acclimatization. She shows that raising or lowering the temperature of 

 Planaria alters the rate of metabolism, but that continued exposure to high or low 

 temperature is accompanied by a gradual return to the original rate. 



In spite of the large amount of work done on temperature tolerance, the methods 

 employed have been so varied that there seems to be no satisfactory way of com- 

 paring, quantitatively, the results obtained by the various workers, and hence there 

 is no basis for an accurate comparison of different animals. The purposes of the 

 present study are as follows: 



1. To find a method of studying, quantitatively, the changes in tolerance pro- 

 duced by acclimatization, which will be applicable to a wide variety of kinds of 

 animals. 



2. By the use of this method to determine, for each of several different animals, 

 the relative amounts by which the tolerance of high temperatures can be modified, 

 and to see whether the power of adjustment bears any definite relation to the ecology 

 of the animals and to their taxonomic position. 



3. To afford, by the work on tolerance, a point of departure for further experi- 

 ments on the physiological nature of acclimatization. 



This work was undertaken at the suggestion of Prof. A. S. Pearse, to whom the 

 writer is under great obligation for advice and assistance. The writer is, indebted to 

 Dr. J. R. Roebuck and to Dr. F. G. Hall for suggestions regarding construction of 

 apparatus, and to Dr. Willis H. Rich for reading and criticizing the manuscript. 

 The work was supported, in part, by funds provided by the Bureau of Fisheries. 



Five species of animals were used in these experiments — the yellow perch, 

 Perca Jlavescens (Mitchill); the large-mouthed black bass, Micropterus salmoides 

 (LacSpede); the bluegill, Lepomis incisor (Mitchill); the sunfish (pumpkinseed), 

 Eupomotus gibbosus (Linnaeus); and the tadpoles of the toad, Bufo americanus Le 

 Conte. 



GENERAL PLAN OF THE EXPERIMENTS 



MATERIAL 



