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ever, for upon removal after three weeks to ordinary water they 

 sprouted, although their development was somewhat abnormal. 

 In other studies the rate of development of frogs' eggs decreased 

 as the concentration of D2O increased from 5 per cent to 30 

 per cent (35) and the development of fertilized sea urchins' eggs 

 was promptly arrested when they were placed in contact with 

 99.5 percent D2O (17). 



Neither bacteria nor lower plants are immune to the action 

 of D2O. Species of luminous bacteria and of Euglena failed to 

 grow in concentrated heavy water, but it was observed that 

 transfer to ordinary water after forty-one and nine days, re- 

 spectively, resulted in renewal of normal growth (11). Other 

 investigators found that different species of unicellular green 

 algae did not grow if the D2O content of the nutrient solution 

 exceeded 85 per cent, although cells survived exposure to high 

 concentrations for several days and resumed growth when re- 

 turned to culture media with low concentrations (25). Fungus 

 mycelia behaved similarly (13). The spores of the fungus that 

 produces the powdery mildew disease of wheat also proved to 

 be useful in a detailed study of the influence of D2O on growth 

 (22a). Elongation of the germ tubes was studied in concentra- 

 tions ranging from 0.02 to 100 per cent. It was found that D2O 

 reduced the maximum rate and final amount of growth, that elon- 

 gation of germ-tubes was promptly arrested when spores were 

 placed in 100 per cent D2O, and that spores were more sensitive 

 to the deleterious action of D2O after growth had begun in H2O. 

 Practically no growth occurred when the D2O concentration 

 was greater than 75 per cent. 



Within certain limits of time, spores were not killed by ex- 

 posure to 100 per cent D2O, since upon return to H2O they re- 

 sumed growth. It was clear, however, that the injury resulting 

 from prolonged exposure was, at least in part, irreversible. With 

 exposures ranging from 24 to 124 hours, the length which germ 

 tubes attained and the duration of the growth period in H2O 

 were inversely related to the previous period of immersion in 

 100 per cent D2O. 



Since high concentrations of D2O exert a marked depressing 

 action on normal growth, several investigators have tested this 

 agent as a possible tool to be used in the treatment of cancers 

 and other abnormal growths. Their efforts have all been unsuc- 

 cessful. Under the conditions of the experiments, rodent tumors 



