486 Physiology 



Triose-phosphate dehydrogenases of T. hippicujn are sensitive to oxo- 

 phenarsine (194), and the activity of hexokinase also is inhibited by 

 arsenicals in trypanosomes (62, 194, 379). 



The susceptibility of Protozoa to certain antibiotics varies with the 

 species. Eiiglena gracilis var. bacillaris remains viable in concentrations 

 of penicillin at least five times as great as those tolerated by Tetrahymena 

 geleii and the difference in resistance to streptomycin is of the same 

 order (330). Tyrothricin, in chickens, has shown parasiticidal activity 

 against extracellular merozoites of Plasmodium gaJUnaceum (544). Aureo- 

 mycin likewise has shown activity against Entamoeba histolytica (374), 

 and comparable effects have been reported more recently for terramycin 

 (Chapter XI). One of the most interesting effects reported so far is the 

 bleaching action of streptomycin on certain green flagellates, first reported 

 in Euglena gracilis var. bacillaris (468). The effect, which involves a loss 

 of the ability to synthesize chlorophyll, presumably is the result of specific 

 damage to certain enzyme systems. 



As mentioned above for pantothenic acid, pteroylglutamic acid and 

 nucleic acid derivatives, certain vitamin analogues retard or inhibit 

 growth and oxygen consumption of several Protozoa. In addition to the 

 general interest of such findings and their bearing on the determination 

 of vitamin requirements, the therapeutic value of certain pantothenate 

 analogues in chickens infected with Plasmodium gallinaceum (28) indi- 

 cates that results of practical value may be expected in further exploration 

 of this field. 



Effects of carcinogenic hydrocarbons 



Stimulation of fission by several carcinogenic hydrocarbons has been 

 reported for Paramecium (577), but these findings have not been con- 

 firmed (553). In the only investigation on ciliates in pure culture, Tittler 

 (551) has obtained no evidence that 3,4-benzpyrene, methylcholanthrene, 

 or 1,2,5,6-dibenzanthrene significantly influences growth of Tetrahymena 

 pyriform is. 



EFFECTS OF IRRADIATION 



Irradiation is a tool of potential value in the study of various prob- 

 lems. One of the least explored is the possibility of inducing biochemical 

 mutations in Protozoa, and the prospects grow more intriguing as proto- 

 zoan food requirements become better known. Effects on rates of fission, as 

 well as the immediate and pathological effects of irradiation, have in- 

 terested a number of workers, so that such information is available for 

 a few species. 



Beyond the violet end of the visible spectrum extend the overlapping 

 ultraviolet, X-ray, and gamma-ray spectra. The ultraviolet spectrum in- 

 cludes radiation from wave-lengths of about 390 mjji, (3900 A., or Ang- 



