Thirty-two strains of an infectious filterable agent, with properties that establish it as a virus, have been isolated from a malady of cats. This disease can be readily recognized and differentiated from other feline diseases by blood studies, which make apparent the characteristic profound leucopenia and marked relative lymphocytosis in the absence of thrombopenia and appreciable anemia. (Because the cytological pictures of the bone marrow and blood are essentially similar to those which characterize human agranulocytosis, we have named the disease under study "infectious feline agranulocytosis.") The cytological reaction to the presence of the virus is further characterized by proliferation of the reticuloendothelial cells of the lymph nodes and spleen, and by the formation of intranuclear inclusion bodies in the cells of the gastro-intestinal mucosa, lymph nodes, and bronchial mucosa.
The etiological agent, the virus of infectious feline agranulocytosis, is pathogenic for cats when given by the oral, intragastric, cutaneous, subcutaneous, intraperitoneal, intravenous, and intranasal routes; it can be recovered at the height of the disease from the blood, spleen, liver, lung, intestinal mucosa, nasal secretions, nasal mucosa and turbinates, feces, and urine. The virus appears to be limited in its pathogenicity to the feline species. We found that a variety of animals, as represented by albino Swiss mice, guinea pigs, domestic rabbits, and ground squirrels (Citellus richardsonii Sabine), failed entirely to react to the injection of massive doses of virus. Repeated attempts at infection of these animals regularly failed when the intranasal, intraperitoneal, subcutaneous, and intramuscular routes of inoculation were employed for single doses. The same was true when from four to six transfers in "blind" serial tissue passages were made. Moreover, attempts to propagate the virus on the chorio-allantoic membrane of the developing chick were unsuccessful.
The significance of the facts is discussed in the paper that follows.