212 ROBERT H. HUTCHISON 



sea-water, in Ringer solutions, and in CaClo solutions, conclude 

 that the protective action of these salts is not an osmotic effect, 

 nor a case of antagonistic salt action, but "sl specific effect of 

 the salts of the sea water/' But we are left in doubt as to just 

 what this specific effect is. Indeed the results of experiments 

 described below seem to indicate that, in the case of Paramecium 

 at least, the salts have no specific action, or if so, such specific 

 action depends upon the nature of the medium in which the ani- 

 mal has previously lived. No attempt is made to offer any 

 complete explanation. It is desired merely to set forth the facts 

 as we found them as a modest contribution to the knowledge 

 of the heat-resisting properties of living cells, with the hope that 

 from an ever-increasing mass of data some general law may 

 eventually be worked out. 



The following experiments were carried out during the winter 

 of 1912-13 while working at the University of Pennsylvania 

 under the direction of Dr. M. H. Jacobs. Pure lines of Parame- 

 cium caudatum were used throughout, and the method of test- 

 ing their resistance to heat was the same as that previously de- 

 scribed (Jour. Exp. ZooL, vol. 15, p. 133-134). In testing the 

 effects of salt solutions a small quantity of the medium contain- 

 ing the animals was centrifuged and two drops of the dense mass 

 of animals were transferred with a pipette to 10 cc. of the solu- 

 tion in question. Five drops of this solution containing the 

 animals were placed in each of the small glass dishes used. The 

 dishes were covered and arranged in order on the floor of the 

 blood-serum oven. The experiments were always conducted so 

 that the rise from room temperature to 45°C. was accomplished 

 in about one hour. Beginning at 37°C., or lower if necessary, 

 the dishes were removed consecutively, one for each rise of one 

 degree Centigrade. After at least one-half hour, for possible re- 

 covery, the number of living and dead in each dish was counted 

 and the percentage calculated. From the percentages the 

 curves for the fatal temperature zones and the mean for each 

 curve were worked out in the manner described in a previous 

 paper. Two pure lines of Paramecium were studied in some 

 detail, the one growing in a medium of alkaline reaction, and 



