A quantitative method for following parasite growth in vitro is described. The method is based on the determination of the degree of incorporation of phosphorus into the nucleic acids, in particular desoxypentose nucleic acids, of the parasitized cell. Phosphorus incorporation is measured by utilizing the radioactive isotope, P32.

The degree of phosphorus incorporation into DNA was found to be closely correlated with estimates of parasite growth based on stained film examinations of intact cell preparations. The isotope was likewise found to be incorporated into the DNA of preparations in which the host cell had been disrupted by lysis and the extent of this incorporation also paralleled the impressions gained from smear examinations.

It is suggested that this method provides a sensitive and objective method of studying parasite growth.

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