QUANTITATIVE STUDY OF THE CHANGES PRODUCED BY 

 ACCLIMATIZATION IN THE TOLERANCE OF HIGH TEM- 

 PERATURES BY FISHES AND AMPHIBIANS 



By EDWARD S. HATHAWAY 

 Professor of Zoology, The Tulane University of Louisiana 



J* 



Contribution from the Zoological Laboratory, University of Wisconsin 



CONTENTS 



Page 



Introduction 169 



General plan of the experiments 170 



Details of methods 173 



Results 178 



Limits of tolerance in normal indi- 

 viduals 178 



Page 



Results — Continued. 



Modification of tolerance by accli- 



matization 181 



Behavior at high temperatures 185 



Discussion 187 



Summary 190 



Bibliography 190 



INTRODUCTION 



A great many observations have been made by numerous experimenters on the 

 maximum temperatures tolerated by organisms. In 1895 Davenport and Castle 

 listed thermal death points that had been determined for 69 species of plants and 

 animals; and the number of species studied, especially of microorganisms, has been 

 increased greatly since that time. Quantitative studies on acclimatization as a 

 factor in the tolerance of high temperatures began with the observations of Flourens 

 (1846) and Ehrenberg (1859), who reported organisms living in hot springs at tem- 

 peratures of 85° and 98° C, when closely allied species in the waters of the same region 

 ordinarily were exposed to temperatures no higher than 40° C. Schwartz (1884) 

 and Aderhold (1888) found that Euglena collected in summer ceased activity when 

 the temperature fell to 5° or 6° C, while those collected in winter remained active 

 at 0° C. 



The most notable work on experimental acclimation of microorganisms is that of 

 Dallinger (1880) on flagellates. By gradually raising the temperature of his cultures, 

 he was able, within a period of several years, to change their limits of tolerance from 

 23° to 70° C. Jollos (1921) has shown that protozoans acclimated to high tempera- 

 tures and to certain chemicals may retain their increased tolerance for many gener- 

 ations in the absence of the acclimating agent. 



Pioneer work on acclimatization of vertebrates was that of Davenport and 

 Castle (1895). They tested the tolerance of toad tadpoles by raising the temperature 

 of the surrounding water at the rate of about 25° C. in 10 minutes, and noted the 



169 



