There have been many examples reported from personal experience to show that influenza is transmitted from man to man. Two objections, however, have had to be met, before this view was generally accepted. First, it has been claimed by some that the disease spread more rapidly from an assumed focus than individuals could travel, and second, that instances were on record of cases occurring spontaneously in isolated communities. Yet a third argument formerly raised against the contagious character of the disease was the claim that it broke out in mass attacks, that large numbers became ill on the same day without the occurrence of isolated antecedent cases. The splendid work of epidemiologists following the 1889 epidemic appears to have answered all of these objections. Many, such as Leichtenstern, have gone into great detail on this subject. In fact, at that time this was the question of greatest importance. Today we assume the correctness of the hypothesis, and pass on to consideration of other subjects of more recent development. We will, therefore, review very hurriedly some of the evidence quoted to prove that influenza is transmitted only from man to man and only by human intercourse. _Isolated places._—Has it ever been shown that individuals completely isolated from communication with communities where influenza is present have, during an epidemic, developed the disease? Leichtenstern, after a comprehensive review, concludes as follows: “We have not a single example on record where influenza has attacked individuals in completely isolated localities, as on mountain tops and mountain passes. Study of this has been undertaken in Switzerland by F. Schmid. The same has been true of ships at sea, as has been shown chiefly from the English Marine Reports. There have been reports of influenza occurring in mid-ocean and particularly in the earlier epidemics, but the information has been insufficient.” Parkes at even an earlier period observed: “I cannot but consider that we require better evidence of ships being attacked in mid-ocean. In some of the quoted instances the ships had been at a port either known to be infected or in which influenza was really present, although it had not become epidemic. As we are ignorant of the exact period of incubation some men may have been infected before sailing.”