TOLERANCE OF HIGH TEMPERATURES BY FISHES, ETC. 181 



used were divided into three classes — (1) those having hind legs in various stages of 

 development but no visible front legs, (2) those having four legs visible but not yet 

 beginning to resorb the tail, and (3) those in which the tail was being lost. Many 

 times, in the work on the two-legged stage, young or retarded individuals were 

 included in the same trials with those that were farther advanced in development, 

 and there seemed to be no appreciable difference in heat tolerance between them; 

 but about the time of the appearance of the front legs there was a sharp fall in the 

 resistance, and this became still more marked as the tail was being resorbed. Evidence 

 on this point was obtained by special trials conducted on individuals in the later 

 stages of metamorphosis, the data being presented in Table 3 and Figure 6. 



Table 3. — Maximum temperatures, in degrees centigrade, tolerated for various lengths of time by 

 normal toad tad-poles in various stages of development 



Stage of development 



24-hour 

 tolerance 



4-hour 

 tolerance 



1-hour 

 tolerance 



15-minute 

 tolerance 



4-minute 

 tolerance 



Two legs - 



36.2 



37.3 



37.4 



38.6 



39.3 





34.2 



35. 1 



36.9 



38.0 



38.0 





34.0 



34.7 



35.3 



35.3 



36.0 



29 30 31 32 33 34 35 36 37 38 39 40° 



To rule out asphyxiation as a possible cause of death of the most advanced 

 individuals, solid objects were supplied on which they could crawl out and get 

 air. The data indicate that for 

 each of the five time periods the 

 tolerance limits of the three stages 

 of tadpoles fell in the same order — 

 namely, two-legged individuals 

 highest, early four-legged stage 

 intermediate, and those losing their 

 tails lowest. 



— 



MODIFICATION OF TOLERANCE 

 BY ACCLIMATIZATION 



In making determinations of 

 tolerance on individuals that had 

 been exposed to temperatures of 

 30° C. (86° F.) and 10° C. (50° F.) 

 the same methods of procedure and 

 computation were used as in the 

 case of normal individuals. The 

 details of the results are shown in 

 Figures 2, 3, 4, 5, and 7 and in 

 Tables 4 and 5, while Figure 9 

 compares the results secured with 

 the various animals. 



24 hours 

 Perch 

 Bass 



Blueglll 

 Sunflsh 

 Toad tadpole 



4 hours 



Perch «.„ 

 Bass 



Blueglll 



Sunflsh *- — 



Toad tadpole ~~ 



1 hour 

 Perth 



Bass ""-•.^ 



Blueglll 



Sunflsh 



Toad tadpole ~ 



15 minutes 

 Perch 



Bass _ 

 Blueglll 



Sunflsh **• 



Toad tadpole - , 



4 minutes 

 Perch 



Bass "* 



Blueglll • 



Sunflsh •'_ 



Toad tadpole * 



Fig. 8. — Averages of maximum temperatures tolerated for various lengths 

 of time by normal individuals of different species. Complete data on 

 tolerance of bass and sunflsh for four minutes are not available. In 

 both of these cases the tolerance may be a littlo greater than that shown 



