452 M. E. COLLETT 



'05) upon Paramoecium aurelia, the acids were not used consist- 

 ently at the same concentrations, the temperature varied from 

 16° to 22°, and the method of washing injured the organisms. 

 Weinland ('94) studied the oral epithelium of the frog at 18°, 

 but made up his solutions at 0.001 M in physiological NaCl. 

 Harvey ('14), in studying the cilia of the giant clam, used acids 

 made up to 0.01 N in van't Hoff's solution and worked at a 

 temperature of about 27°. We do not know in these cases 

 whether the salts antagonize the acids (as was found by Loeb, 

 '12, and by Osterhout, '14) or whether they reinforce its action 

 (as found by Paul et al., '10), and consequently are not sure 

 how far these experiments are comparable with other experi- 

 ments in which the acids were made up in distilled water. 

 Neither are Koltzoff's studies ('14) upon the cilia of Carchesium 

 available for comparison, for, unlike the previously mentioned 

 experiments, they deal with concentrations which do not kill 

 the cilia, but only increase their viscidity. 



There are, however, reports upon other material capable of 

 showing specific differences clearly. The experiments of Land- 

 steiner ('13) on acid agglutination of blood corpuscles and of 

 Walbum and of Cunningham ('16) on haemolysis give clear 

 evidence of specific differences in resistance. Ritter ('12) and 

 Clark ('96) found striking differences in resistance among vari- 

 ous mold spores, as did Heald ('96) with seedlings. Taylor 

 ('17) found that the concentration of any acid necessary to clear 

 a wound of bacteria varied with the organisms concerned and 

 that the toxic order likewise varied. This is precisely the condi- 

 tion observed in the present experiments. Similar results have 

 been obtained by Kopazcewski ('14) with enzymes. His obser- 

 vation that the optimal Ph was not the same for his usual prepa- 

 ration of maltose and for a well-dialyzed preparation indicates 

 the importance of salts in determining acid resistance and may 

 perhaps lead to an explanation of certain specific differences. 



