If we consider only those family groups having over 1,000 individuals as being sufficiently large to be representative, we may conclude that families of from three to seven individuals show no progressive increase in influenza incidence with increase in size of the family. But all the available evidence indicates that other things being equal, the age incidence is a very important factor. Its influence will be felt in the subject under consideration, and it will modify the results. Thus, families of one or two are almost invariably adults; families of three are very frequently made up of two adults and a child or infant, while families of from five to seven will be more likely to have a high proportion of young adults—the age period more seriously affected. The next question arising is whether those families, large or small, which are living in crowded circumstances, are more likely to develop the disease. Arbitrary standards must be chosen as indices of crowding. We have chosen two in order that they may check each other. The first is based upon the number of individuals sleeping in a bedroom. Families are classified as follows: Maximum sleeping in a single bedroom, 1; maximum sleeping in a single bedroom, 2; maximum per bedroom, 3, 4, etc. The second standard of crowding is based upon the ratio of the number of individuals in the family and the number of rooms occupied. One person living in one room is not crowded; two in two rooms, three in three rooms, four in four rooms, eight in eight rooms, twelve in twelve rooms, are not crowded. Two people living in one room four in two rooms, six in three rooms, twelve in six rooms, are decidedly more crowded. On the contrary, one individual in two rooms, two in four, three in six, four in eight, five in ten, etc. have an unusual amount of room. The ratios ^P⁄_{R} are then throughout, ¹⁄₁, ²⁄₁, ½. These are used as dividing lines. All families with ratios higher than ²⁄₁ are classed as very crowded. Families with ratios above ¹⁄₁ up to and including ²⁄₁ are classed as crowded. Families with ratios above ½ up to and including ¹⁄₁ are classed as roomy, and those with ratio of ½ or lower are classified as very roomy. Classifying all families in all six districts according to these last four degrees of crowding, we find, as is shown by Table V, that there is a progressive increase in the proportion of families with one or more cases of the disease, with increase in the extent of crowding.