For most of these autopsies there is a record of the date of onset of the illness, namely, influenza, which finally resulted in pneumonia and death. Comparison of the number of cases of influenza which developed on any day with the number of fatal cases which had their onset on the same day will determine the mortality of influenza at different periods of the epidemic. Chart 1 shows the number of cases of influenza which had their onset on each day from September 1 to October 31 and the number of fatal cases with autopsy which had their origin on corresponding days. The comparison by weeks between autopsies and total number of deaths shows that the autopsies represent with considerable accuracy the deaths. If there is any error it occurs at the height of the outbreak of pneumonia from September 29th to October 5th and not at its beginning, or end. The chart shows that the highest mortality occurred among cases of influenza which had their origin at the beginning of the epidemic from September 21 to October 1, whereas after October 1, though the maximum number of cases of influenza occurred on October 3, very few developed fatal pneumonia. =Mortality from Pneumococcus and Streptococcus Pneumonias.=—By referring fatal cases of streptococcus pneumonia back to their date of origin it is possible to determine what proportion of the cases of influenza, which developed on any day, died with infection by hemolytic streptococcus. The accompanying chart (Chart 1) shows that infection with hemolytic streptococci has been very frequent at the beginning of the epidemic of influenza (shown by area with double hatch in chart) that is, from September 20 to 30 and subsequently has gradually diminished so that few cases have had their onset in the second half of the epidemic from September 30 to October 15. Pneumococcus pneumonia uncomplicated by streptococcus infection (shown by area with single hatch in chart) pursued a course which more closely conformed to the curve representing influenza. The cases of influenza which resulted fatally bore a fairly constant ratio to the total number of cases of influenza from the onset of the epidemic until October 1, but subsequently few cases of influenza developed fatal pneumococcus pneumonia. These charts arranged with reference to the onset of fatal pneumonias dissociate very clearly the outbreak of streptococcus pneumonia, which reached its height at the beginning of the influenza epidemic, from the uncomplicated pneumococcus pneumonia which reached its maximum at the midpart of the influenza epidemic and then abruptly abated. [Illustration: