Jordan and Sharp have obtained statistics regarding approximately 4,000 men at the Great Lakes Naval Training Station. The men’s statement regarding previous influenza was accepted whenever the attack was said to have occurred during the influenza period of 1918–1919, _i.e._, in September, October, November, December, January, February and March. The great majority were reported for the period of September to December. Only a few cases were reported as occurring in March, and perhaps these actually occurred somewhat earlier than the men recalled. A few cases were accepted as influenza when reported as occurring in Europe during July and August, 1918. They found that 28.5 per cent. of 3,905 men had had the disease in 1918, and that 22.6 per cent. were attacked in 1920. Of those who had the disease in 1918–19, 21.2 per cent. had a repeated attack in 1920, while of those who had not had a previous attack, 23.1 per cent. were attacked in 1920. A similar study among 2,472 men at Camp Grant showed that 15.8 per cent. had had influenza in 1918–19, and 11.7 per cent. in 1920. Of those with previous influenza history 15.6 per cent. had a repeated attack, while of the remainder without previous history of influenza 10.9 per cent. were attacked in 1920. They conclude that no marked immunity to influenza exists 12 to 15 months after a previous attack, but that the results do not show that some degree of immunity may not obtain at an earlier period. It is interesting while considering the subject of immunity to pay particular attention to those who _did not_ develop the disease as well as to those who did. In our series 70 per cent. of all individuals escaped the disease in both epidemics. With some variation this figure will hold for all communities. Or, again, among those who had the disease in 1920, 75 per cent. _had not had it_ in the preceding waves. Hall states that in Copenhagen at the Bispebjaerg Hospital, among the 500 patients with influenza in the four weeks early in 1920, 91.8 per cent. _had not had_ the influenza during the 1918–19 epidemic. H. F. Vaughan found in a review of 2,500 cases occurring in Detroit in January, 1920, that _84 per cent. had never had_ the influenza before. The true significance of these figures cannot be recognized, because we are not informed as to the per cent. of these populations attacked in 1918–19. We observed such a universal distribution of influenza during the epidemic period that it is frequently assumed that all individuals are exposed to the disease, that the virus must enter the body of all or nearly all, and that it is due chiefly to a relative natural immunity that some do not fall victims. Is this the actual state, or is it true that the distribution of the virus is limited to about one-third of the population and that practically all of those who are actually exposed develop the disease? These are the two extremes; more probably the actual state is somewhere between.