It is therefore evident that just as "no chain is stronger than its weakest link," so in the broad sense no community is stronger than its weakest group of individuals, and pneumonia, like other epidemics, may be well described as the vengeance which the "submerged tenth" may wreak from time to time upon their more fortunate brethren. Now that we know that under decent and civilized conditions of light and ventilation the pneumococcus will live but an hour to an hour and a half, this reduces the risk of direct infection under these conditions to a minimum. It is obvious that the principal factors in the control of the disease are those which tend to build up the vigor and resisting power of all possible victims. The more broadly we study the disease the more clearly do the data point in this direction. First of all, is the vivid and striking contrast between hospital statistics and those gathered from private practice. While many individuals of a fair wage-earner's income and good bodily vigor are treated in our hospitals, yet the vast majority of hospital patients are technically known as the "hospital classes," apt to be both underfed, overworked, and overcrowded. On the other hand, while a great many both of the very poor and even of the destitute are treated in private practice, yet the majority of such cases who feel "able to afford a doctor," as they say, are among the comparatively vigorous, well-fed, and well-housed section of the community. And the difference between the death-rate of the two classes in pneumonia is most significant. In private practice, while epidemics differ in virulence, the rate ranges all the way from five per cent to fifteen per cent, the average being not much in excess of ten per cent, occasionally falling as low as three per cent. In the hospital reports on the contrary the death-rate begins at twenty per cent and climbs to thirty, forty, and forty-five per cent. It is only fair to say, of course, that hospital statistics probably include a larger percentage of more serious cases, the milder ones being taken care of at home, or not presenting themselves for treatment at all. But even when this allowance has been made, the contrast is convincing.