As a result of the extensive investigations in America and on the Continent into the relationship of Br. abortus to undulant fever in man, attention in this country has been directed to cases of fever due to obscure causes, with the result that an increasing number of cases of undulant fever are being reported. So far, however, the cases in Great Britain appear to be less numerous than those in the United States and in Denmark where every effort has been directed to tracing sources of infection and where the conclusion has been reached that, although a certain number are infected by contact with the secretions and carcasses of infected animals, many infections occur through ingesting milk containing Br. abortus.