The inhibitory action of sodium sulfadiazine on the growth of psittacosis virus (6BC) in embryonated eggs is readily reversed by citrovorum factor but not by small amounts of vitamin B12.

In embryonated eggs, the pteroylglutamic acid analogues, 9-methylpteroylglutamic acid and 4-aminopteroylaspartic acid, produced some suppression of the growth of psittacosis virus (6BC). 4-Aminopteroylglutamic add, 4-amino-N10-methylpteroylglutamic acid, and 4-aminopteroylaspartic acid inhibited the growth of this virus in tissue cultures at concentrations which were not toxic for the host tissue. The inhibitory action of 4-amino-N10-methylpteroylglutamic acid and 4-aminopteroylaspartic acid was readily overcome by addition of citrovorum factor.

Growth of meningopneumonitis virus in embryonated eggs or tissue culture is suppressed by 4-aminopteroylaspartic acid.

The advantages of the tissue culture technic for studies on the growth of viruses are discussed.

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