Experimental Demonstration of a Strain of the Dog Hookworm, Ancylostoma caninum, Especially Adapted to the Cat

manded most attention is perhaps that of the ascarids of man and of the pig. Enough has been done to indicate that the postulation of physiological strains offers the most plausible explanation of the facts of the epidemiology and distribution of these parasites. Adequately controlled experiments sufficient to satisfy the strictest experimentalist still seem to many to be desirable. Certain difficulties other than the necessity of using man as the experimental animal seem to be involved in this case. This may prove to be true also in the case of attempts to differentiate the trichurids of these same hosts which Schwartz (1926a) has shown to be morphologically identical. Other cases where the same situation has been suspected either have not been tested experimentally or have not yielded readily to this type of treatment. In the case reported here, however, a situation has fortunately arisen which has admitted of relatively easy experimental analysis. In September, 1925, a cat obtained at Cold Spring Harbor, Long Island, died in this laboratory. Fecal examinations had previously shown the presence of hookworm ova, and at autopsy there were obtained 10 typical specimens of A. caninum. The contents of the rectum when cultured yielded larvae which upon being fed to a young dog showed a peculiar lack of infectivity. Larvae from the original cultures were fed to cats and the strain has been kept in cats since that time. The series of experiments described below shows that this strain is as well adapted to cats as a strain obtained from a Baltimore dog is adapted to dogs. But either strain is only slightly infective to the species of host other than the one from which it was obtained. The adults of the two strains are morphologically identical. A series of measurements to show the size relations are now being made. The results of these experiments serve to explain some of the peculiarities of the distribution of this parasite. It was previously