SUMMARY: A bacteriophage method of classifying strains of which inhabit the alimentary tract of cattle has been evolved. It was possible to divide the strains into a large number of types by this method. Varying proportions of strains isolated from the faeces of human beings, sheep, pigs and poultry were also typable by the phages employed. This method of phage typing was used to study the origin and behaviour of the population in the alimentary tract of healthy cows and calves, and of calves suffering from white scours, in one self-contained herd (herd A) and to a lesser extent in twenty-seven other herds. Several types of were often found in the same faecal specimen in cases of scouring, as well as in healthy calves. Seventy different phage types were found in the faeces of the healthy calves in herd A, many occurring infrequently. Thirty-two different types were discovered in the faeces of the scouring calves in this herd; only one strain of one type was found in scouring calves that was not found also in healthy calves. Two types were found commonly in the calves but rarely in the cows. The examination of strains of isolated from faeces of cows and calves at daily and weekly intervals indicated that some types usually remained dominant for a week or so and were then gradually succeeded in dominance by other types. In some animals frequent and sudden changes were apparent; in others one type might be the only type isolated from the faeces for a number of weeks continuously. Changes of dominant phage-type commonly occurred in faeces of calves during the time they were suffering from white scours. The mother did not appear to be a frequent source from which a calf acquired its ; the calf pens themselves seemed a more probable source. Exceedingly large numbers of were found in the faeces of healthy and scouring calves during the first 14 days of life, a period when white scours occurs; very much smaller numbers were found in older animals. Studies on material from the twenty-seven other herds supported the findings in herd A; many phage types of were found in these herds that had not been found in herd A. The aetiology of calf scours is discussed in the light of these and other observations.


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