The _efficacy of face masks_ is still open to question. Certainly the face mask as extensively used during the 1918 epidemic was of little benefit and in many cases was, without doubt, a decided detriment. The same mask was worn until it was filthy. It was not worn in such a way as to be a protection. Even had the nose and mouth been efficiently protected, the conjunctivae remained unprotected. The work of Maxcy and of Vincent and others has demonstrated the importance of the naso-lachrymal duct as a possible portal of entry into the respiratory tract proper. After cultures of Bacillus prodigiosus were sprayed upon the ocular conjunctivae these organisms have been recovered from the nose within five minutes, from the nasopharynx within fifteen minutes and from the feces within twenty-four hours. One difficulty in the use of the face mask is the failure of co-operation on the part of the public. When, in pneumonia and influenza wards, it has been nearly impossible to force the orderlies or even some of the physicians and nurses to wear their masks as prescribed, it is difficult to see how a general measure of this nature could be enforced in the community at large. If masks are to be used they should be employed in the same manner as for protection against the plague. They should be made to cover the entire head. This procedure has been recommended particularly by Vincent and by Thorne. It is safe to say that the face mask as used was a failure. _Problems for the future._ _Constructive research._—While pure epidemiologic study of influenza will not demonstrate the causative agent, it is the chief procedure upon which we can at present rely for improvement in our methods of combat. Many important laboratory contributions have been made during the last two years. The majority have been without immediate value to the health officer. The author suggests in the following paragraphs a plan of study, based upon past epidemics and the experiences of the last pandemic, as epitomized in the preceding chapters. During the exposition of this subject we have drawn certain conclusions and have developed some theories. We believe that they explain the facts correctly, but should the hypotheses prove not entirely correct the value of the following outline for study will be in no way impaired.