TOLERANCE OF HIGH TEMPERATURES BY FISHES, ETC. 



173 



26 per cent of survivals at 34° indicates that out of the 86 per cent that survived 

 at 32°, 26 per cent would have survived at 34°. Hence, Pi = 26 and P 2 = 60, and T 

 equals approximately 32.3°. The advantage of this average tolerance limit over 

 the simpler majority limit, as a basis for measuring acclimatization, is illustrated 

 in Table 1, which shows that the majority tolerance lies distinctly below that of the 

 average in the cases of bass and toad tadpoles, and decidedly above it in the case 

 of the perch. 



Table 1. — Maximum temperatures tolerated for 2-1 hours by a majority and an average of normal 



individuals 





Majority 



Average 



Perch 



° C. 



30 

 32 

 34 

 34 

 36 



0 a 



29.6 

 32.2 

 34.0 

 34.0 

 36.3 





Bluegill. 









METHOD OF ACCLIMATIZATION 



In attempting to test the relative ability of various animals to become accli- 

 mated, it was decided to make the following determinations for each species : 



1. The tolerance limits of individuals that had been living at room temperature. 

 These individuals are referred to as normals. 



2. The extent to which tolerance limits were raised by exposure for varying 

 lengths of time to a temperature of 30° C. 



3. The extent to which tolerance limits were lowered by exposure for varying 

 lengths of time to a temperature of 10° C. 



The temperature in the aquaria in which the normal animals lived averaged 

 between 22° and 23° C. The members of all the different species showed decided 

 stimulation when transferred to 30° C, and a temperature of 10° C. was low enough 

 to decrease activity and feeding very markedly. 



The acclimatization periods used for fishes were 1 day, 4 days, and, when prac- 

 ticable, 16 days. In the work on toad tadpoles, periods of 1 hour, 4 hours, 1 day, 4 

 days, and 8 days were employed, development occurring too rapidly to permit the 

 use of 16-day periods with the individuals available. 



DETAILS OF METHODS 



APPARATUS 



The principal pieces of apparatus used consisted of (a) a cold box, which was kept 

 at about 10° C; (b) a series of seven constant-temperature baths, adjustable for any 

 desired heat above room temperature; and (c) an aeration system, by which air was 

 bubbled through the jars of water containing the fishes. 



The cold box consisted of outer and inner wooden cases, inclosing an outer and 

 an inner sheet-iron tank. The jars containing the specimens stood in water in the 

 inner sheet-iron tank, which, in turn, was surrounded by the water filling the outer 

 tank. Insulation was furnished by the inner and outer wooden cases, the double 

 glass doors of which permitted good illumination. The baths for use at higher 



