It is characteristic of human enthusiasm and hopefulness that each raiding party prays that it may bring back with it a general officer, a field marshall, the one who is chiefly responsible for the enemy offensive. In our own little battle with our invisible host we have long since discovered that field marshalls here as elsewhere are difficult to discover by raiding parties. But the raids are and should be made just the same. They almost invariably bring back some new item of information, and it is the experience of many wars that even though the commanding general be never captured, repeated small or large attacks following preliminary reconaissance, if diligently and valiantly prosecuted under good leadership may win the war. In studying the life and habits of the influenza virus and its army of secondary invaders, and the results thereof in small groups composed of individuals as the unit, instead of large groups with communities as a unit, we will be able to discover a certain number of additional facts, some of which may have considerable value. In the study by the author of six selected districts in Boston a special study was made of the occurrence and manner of spread of the influenza in the household or family as a unit. The 10,000 individuals canvassed were distributed through 2,117 families. Of these two thousand odd families, 45.44 per cent. were visited with one or more cases of the disease in the 1918–19 epidemic, and 27.25 per cent. in the winter of 1920. Of these, 14.31 per cent. had cases in both epidemics. In either one or both of the two epidemics under consideration, 58.38 per cent. of all families had influenza (see Table III). TABLE III. _Per cent. of families invaded by influenza._ ═══════════════╤═════════════╤═════════════╤═════════════╤═════════════ Boston District│ 1918–19. │ 1920. │ 1918–19 and │ Total. No. │ │ │ 1920. │ ───────────────┼─────────────┼─────────────┼─────────────┼───────────── 1 │ 49.59│ 32.79│ 20.05│ 62.33 2 │ 36.04│ 17.36│ 7.25│ 46.15 3 │ 45.89│ 26.43│ 14.71│ 57.61 4 │ 48.48│ 32.20│ 14.39│ 66.29 5 │ 52.48│ 34.11│ 19.53│ 67.06 6 │ 43.16│ 24.21│ 11.23│ 56.14 All Districts │ 45.44│ 27.25│ 14.31│ 58.38 ───────────────┴─────────────┴─────────────┴─────────────┴───────────── Explanatory note: 45.44 per cent. of all families were invaded in 1918. 27.25 per cent. of all families were invaded in 1920. 14.31 per cent. of all families were invaded in both epidemics.