Abstract
1. The association of the α type of Bact. coli, an organism similar to Bact. neapolitanum or to D433 Taylor, Powell and Wright, with gastro-enteritis of infants is further confirmed.2. A new type of Bact. coli called the β type and differing from the α type in certain of its cultural characteristics and antigenically is described as also associated with cases with similar symptoms.3. The antigenic structure of the α and β types has been examined, and both types show a well-marked specificity.4. Either organism can be readily isolated from faeces during an acute phase of the disease, but there may be some difficulty in recovering either during a subacute stage.5. Both organisms usually disappear from the intestinal contents as convalescence is established, but a certain number of cases have been discharged still carrying them.6. These organisms can rarely be found in faeces from infants ill with diseases other than infantile gastro-enteritis, or in specimens from adults. When they are found the cases from which they were isolated have usually some history of contact with gastro-enteritis.7. The actual significance of the association of these organisms with gastro-enteritis has not been determined, but their isolation points to a diagnosis of infantile gastro-enteritis.8. In cubiclized and open wards the examination of faecal specimens for these organisms provides a means of controlling nursing technique and determining whether or not intestinal cross-infection has occurred.