THE EFFECTS OF CERTAIN SALTS, AND OF ADAPTA- 

 TION TO HIGH TEMPERATURES, ON THE HEAT 

 RESISTANCE OF PARAMECIUM CAUDATUM 



ROBERT H. HUTCHISON 



From the Zoological Laborntory of the University of Pennsylvania 



ONE FIGURE 



EFFECTS OF SALTS ON HEAT RESISTANCE 



The effects of certain salt solutions in increasing the resist- 

 ance of various animals to heat are sometimes quite marked, 

 and it seems probable that all animals of aquatic habit would be 

 similarly affected under the proper conditions. Loeb and Was- 

 teneys (Jour. Exp. Zool., vol. 12, p. 543), found that salts exerted 

 a great influence on the ability of Fundulus to withstand sud- 

 den changes of temperature. The maximum temperature into 

 which these fish could, with impunity, be transferred suddenly, 

 varied with the concentration of the sea-water or of a Ringer so- 

 lution, "being about 25°C. for a concentration of M/128 or 

 M/64; 27°C. for a concentration of M/32; 31°C. for a concen- 

 tration of M/8; and almost 33°C. for a concentration of M/4." 

 Dextrose solutions were found to lack this protective effect 

 against a sudden rise of temperature. 



In a previous paper (Jour. Exp. Zool., vol. 15, p. 143) the 

 writer mentioned a few experiments in which the heat resistance 

 of Paramecium caudatum was increased when the animals were 

 transferred to solutions of NaNOs, NaCl, and KNO3, the whole 

 death temperature curve being shifted two degrees higher on the 

 scale. 



The results of experiments of this kind have never been satis- 

 factorily interpreted, and there is still lacking a complete expla- 

 nation of the protective action of salts against heat, and of the 

 acclimatizing effect of exposure to moderately high temperatures. 

 Loeb and Wasteneys from their experiments with Fundulus in 



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THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 19. NO. 2 



