More and more attention has been directed in recent years toward the problem of the prevention and control of the acute respiratory diseases of infancy and childhood. According to a survey made by the Chicago Pneumonia Commission,1the prevalence of these infections has caused more deaths than all other infectious diseases combined, outranking in mortality even the diarrheal disorders. Whereas the death rate from enteric infections has steadily decreased, that from the acute respiratory diseases has remained stationary, so that the winter peak has come to exceed the summer peak of mortality. In view of this situation it is evident that there is an urgent need for a careful analysis and proper evaluation of the various factors which induce acute pulmonary infections in infancy and childhood, Vital statistics reveal the incidence only of the severe forms of respiratory disorders and do not give any indication as to the frequency