A method is described for infecting groups of cotton rats with relatively constant numbers of the filarial worms, Litomosoides carinii, all of which are of the same age. The infections were produced by exposing the rats in metal tanks to counted numbers of mites whose percentage of infection had been determined. Such rats are superior for chemotherapeutic studies and for studies on immunity to wild caught rats with infections of various numbers of worms of mixed ages. Further improvement along this line is needed, however, and to indicate possible lines of procedure the factors in the variability observed in these experiments are analyzed.
Department of Preventive Medicine and Public Health, University of Texas School of Medicine, Galveston, Texas.