them and to make the best use of details of information obtained by scouting parties below. It is to be hoped that at no very distant date a survey of the top of the mountain will thus become an accomplished fact. Meantime, those who cannot fly may find useful employment in examining the track beyond the farm. There is the chance there of picking up facts relating to such questions as the ‘parasites associated with a parasite,’ symbiosis, and the like; take, for example, a suggestion made fourteen or fifteen years ago that the influenza organism may at one time live in association with Pfeiffer’s bacillus, at another with the Micrococcus catarrhalis, and so on; or the throat distemper organism may be yoked now with the diphtheria bacillus and now with the Streptococcus conglomeratus. (Is that, I wonder, now to be regarded as a concept or as an occurrence or happening?)” At best our knowledge of the cause and manner of spread of influenza is fragmentary and insufficient. Attempts to outline a system of control and prevention based upon present concepts are met with many discouragements. The next pandemic will not be prevented. The disease will surely return. If the interval be sufficiently long it may find us quite as unprepared as we were in 1918. Discouraging as the outlook is there are many bright points upon which we must base our hopes for future results. The difficulties are many: First the _diagnosis_ of influenza is difficult either in the individual case or in the form of a mild epidemic. Even in 1918 the identification was often not definitely made until after weeks had elapsed. Second, we know little concerning the _mode of transmission_ of the disease. We speak of “respiratory infection.” We believe that the transmission is by a mechanism similar to that for measles, but we have never experimentally transmitted either disease. The _short incubation period_ places us at a great disadvantage. Were the interval between the occurrence of the first case and the development of additional cases as long as it is in measles, the problem of isolation and quarantine would be simplified. As in measles the disease is probably _very early infectious_, presumably before acute symptoms develop. The majority of cases of influenza are _ambulatory_. Many individuals do not take to their beds, but continue about their work, spreading the disease wherever they go. Again, we are ignorant of the _period of infectiousness_. Dr. Meredith Davies has made observations indicating that a patient becomes non-infectious within one week after the temperature has become normal. How many influenza patients remain isolated throughout this period? A _carrier state_ probably exists and plays a most significant part in the spread.