270 



The Ohio Journal of Science [Vol. XXI, No. 8, 



It will readily be seen from the table that the tolerance of 

 different individuals of the same species is not necessarily the 

 same. Some of the Euglena deses, for example, succumbed to 

 the .05%, while the rest were killed by the .1%. In Euglena 

 gracilis the variability in this regard is very great, a fact shown 

 by Zumstein's results also. Similar physiological variability 

 among the individuals of a species and even in the same culture 

 is a phenomenon which the writer has repeatedly observed in 

 connection with factors other than acidity. Its significance 

 remains to be shown. 



TABLE I. 

 Percentages of Citric Acid Causing Death Within 24 Hours. 



* — Some, but not all, dead. 

 X— All dead. 



The most striking fact brought out by a perusal of the 

 table is the remarkable difference between Euglena gracilis 

 and all the other species. Thus the species first studied in this 

 connection, and assumed by various writers to be typical of the 

 other species of its group, is seen to be decidedly exceptional 

 when compared with the six other forms that have been tested. 



One discrepancy between these results and those of Zum- 

 stein may be noted. All the individuals of Euglena gracilis in 

 the 5% solution were found dead; while Zumstein states that a 

 few remained alive in 5 and 6%. In view of the great variabil- 

 ity which we have noted in this species, and the relatively small 



