1.This paper presents experimental evidence showing the behavior of strains of Strongyloides obtained from primate hosts and from human hosts.
2.Previous studies by the writer have demonstrated the different capacities of macaque, ateles and human strains of Strongyloides to establish themselves in autochthonous and reciprocal hosts. This investigation presents evidence based on inoculation of man, the macaque and the dog with chimpanzee, macaque, capuchin and human strains.
3.Repeated passage of pure type human strains through canine hosts invariably produced alterations. These tended to simplify themselves into the direct type of development. Passage of the chimpanzee strain through dogs failed to modify it from the original indirect type, but in man the stability was reduced. The organism bred true to type in the macaque but after this passage was unable to develop in dogs.
6.Change from the hyperinfective and indirect types to the direct type was accompanied by a decrease in the virulence of the organism and increased failure to establish itself in the canine host. This is in direct contrast with the increased virulence and greater ease of establishing itself in the case of the unmodified chimpanzee strain during successive passages through dogs.
5.The data established by this investigation provide proof as to the instability and variability of the several strains of Strongyloides studied.
Contribution from the Parasitology Laboratory, Department of Tropical Medicine, Tulane University, New Orleans, La. Assisted by a grant from the Committee on Scientific Research of the American Medical Association. Read before the American Society of Tropical Medicine, Birmingham, Alabama, November 16, 1932.