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Eight chimpanzees were fed and/or inoculated with a single Coxsackie (C) virus or combinations of different ones. The responses in terms of complement-fixing (c-f) antibodies to 6 to 10 such viruses were measured throughout periods of 1 to 2 years. Although the animals usually responded with rises in homologous antibodies after the feeding or the inoculation of viruses of special immunological types, a variable number of heterologous c-f antibodies were observed to increase significantly at the same time. When immune animals were challenged with homologous virus, they failed to become virus carriers again and no rises in neutralizing antibodies were detected. However, the challenge usually resulted in a boost in the titer of the homologous c-f antibody and often of heterotypic c-f antibodies. This was particularly striking in those chimpanzees in which the c-f antibody had fallen below a detectable level. In contrast to this, the infection of chimpanzees with agents outside the Coxsackie family (poliomyelitis viruses and Egyptian strains of West Nile virus) failed to influence the level of Coxsackie antibodies even during the periods when c-f antibodies to these non-Coxsackie viruses were rapidly rising.

A hitherto unreported disease of infant mice is described. The agent reproduces upon passage, is filterable, is confined mainly to the gastrointestinal tract in infant and adult mice, causes death in infants and inapparent infection in adults, and is sensitive to mild heat, ether, and sodium deoxycholate. Unique and characteristic morphologic changes occur in the epithelial cells of the intestine in infected infant mice. These consist in the development of multinucleated giant cells designated "balloon cells.".

The preparation of complement-fixing antigens for the Coxsackie group of viruses (C virus) is described. This includes the manufacture of crude antigens, their subsequent treatment with protamine sulfate to remove non-specific interfering substances, and their concentration by ultracentrifugation. The plate complement fixation technique of Fulton and Dumbell is described in detail as it has been used for the Coxsackie viruses. Seven strains of C virus have been cross-tested in the plate complement fixation test and have been found to belong to six immunologically distinct types. The temporal pattern of complement-fixing antibodies in human beings infected with two types, Ohio-1 and Easton-2, respectively, has been studied. In the former the antibodies rise to a peak rather late in convalescence (3rd month) and in the latter, complement-fixing antibodies are already present at high levels in the acute phase serum. The problems of serodiagnosis are briefly discussed.

Transmission experiments have shown that epidemic diarrhea of infant mice of the CFW strain is infectious and communicable. Cage to cage spread can take place by the air-borne route. The agent appears to be a fairly heat-resistant virus that can be serially transferred and that is neutralized by specific hyperimmune antiserum from rabbits. Mice are susceptible to it by the oral route from at least the 3rd day after birth to the 10th or 11th day. Thereafter they appear to become resistant. The shortest incubation period observed has been 40 hours from the time of feeding infectious material; the longest period could not be ascertained under the conditions of test. Factors relative to the differentiation of this virus from other viruses are briefly discussed.