THE COMPARATIVE RESISTANCE OF DIFFERENT 

 SPECIES OF EUGLENIDAE TO CITRIC ACID.* 



W. J. KOSTIR, 

 Ohio State University. 



In the course of his experiments on the nutrition of Euglena 

 gracilis, Zumstein (1900) discovered that this species is able to 

 tolerate surprisingly high concentrations of certain organic 

 acids. He made use of this fact to obtain cultures free, or nearly 

 free, from bacteria. Adding various proportions of the acid to 

 the culture medium employed, he found that while the multi- 

 plication of bacteria was effectively inhibited, rich cultures of 

 apparently normal Euglenae could be obtained. Ternetz (1912) 

 working with the same species, also made use of this method. 



Of several organic acids experimented with, Zumstein found 

 citric acid to be the least harmful to this organism. He reports 

 that solutions of 0.5 to 2% are "not injurious," and that cul- 

 tures to which these percentages of the acid had been added 

 were quite successful. Whether all the individuals used in 

 inoculating these cultures survived the transfer to the acid 

 medium is unfortunately not clear from Zumstein's account. 

 In the case of "3 and 4%," he states that many individuals 

 remained living even after 88 hours. In "4 and 5%" many 

 were actively moving after five days. In "5 and 6%" a few 

 remained alive even after 17 days. Higher concentrations were 

 apparently found to be uniformly fatal, though Zumstein makes 

 no definite statement as to the lowest percentage sufficient to 

 kill all the individuals exposed to it. 



Unfortunately, the results of these experiments ' have been 

 interpreted by the writers of certain text-books and manuals in 

 a way not at all justified by the facts. Results obtained on a 

 single species have been made the basis for generalizations 

 concerning the whole genus Euglena, and even the family 

 Euglenidas. Prowazek, in his "Einfuehrung in die Physiologic 

 der Einzelligen" (1910), Lemmermann, in the section on the 

 Euglenidai in "Die Suesswasserflora Deutschlands, Oester- 

 reichs, und der Schweiz" (1913), and Doflein, in the fourth 



* Contribution Xo. 66 from the Department of Zoology and Entomology, 

 Ohio State University. 



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