We can compare the epidemic features of influenza with these other contagious diseases, but we will always find some points of difference from one or another. Let us consider again for a moment epidemic meningitis. There is no combination of predisposing causes, environmental, meteorologic or bacteriologic which will produce epidemics of cerebrospinal meningitis in the absence of the meningococcus itself. The organism causing the disease must be present before the disease will occur. The specificity of the invading organism in the different diseases will always produce some variation among the epidemiologic features. Other things being equal, that locality in which this germ is most extensively distributed will be the locality in which epidemics, when they do break out, will be most extensive. In the case of our army camps, those individuals carrying the disease virus from the endemic foci to the camps were not the ones who fell ill. Generally it was those, coming from other areas in which meningitis was not extensively distributed and who had, therefore, not acquired an increased resistance to the disease, who fell ill. But after the disease had acquired increased virulence at Camp Jackson, not only did it occur in the troops at that camp, but it also became quite extensive throughout the civilian population, presumably among those who had previously been exposed to it in its endemic form. In our comparison of influenza with other infectious diseases we wish to show particularly that the disease is not in a class by itself, but that its epidemiologic features are not unlike those of other respiratory infections, that the manner of spread and the mode of infection are similar to those of the other diseases. Nothing unusual or unknown need be called into use in explaining any differences. Those differences that very palpably exist can be explained by facts which we already know. Leichtenstern, thirty years ago, believed that the disease was similar in its manner of spread to other infectious diseases. He observed this particularly in the earliest and the latest phases of epidemic spreads where cases were scattered. He saw that in households the disease attacked some and spared others even of those intimately connected with the sick, just as was the case in diphtheria or meningitis. He writes: “Comparing these later periods the disease evidences the same contagious characteristics as the other endemic contagious diseases, such as scarlet fever, measles, diphtheria, epidemic cerebrospinal meningitis, etc.” Parkes made very similar observations even before the 1889 epidemic. _Measles._—A comparison of influenza and measles will offer some explanation of the differences between the epidemic constitution of the former and that of the other respiratory diseases.