The negative results occurred in seven cases. In three of these (749, 750, 756) B. coli overgrew the cultures from the bronchus, in two also from the lung, and in one, without lung culture, from bronchus and pleural cavity. The mere presence of B. coli, however, did not preclude the isolation of B. influenzæ, as is seen in cases 746, 758, 761 and 765. The finding of B. coli would suggest a post-mortem invasion. The hours after death before the autopsy was done were in these seven cases, ½, 15, 6, 18, 16, 19, 16, respectively. That delay in performing the autopsy, as emphasized by Spooner, Scott and Heath, adds to the difficulty is self-evident, but successful isolations of B. influenzæ have been obtained after even longer periods than in the negative cases (761). In the fourth negative case (763) the bronchus was not cultured. A pneumococcus was grown from the pleural cavity and no growth was obtained from the lung. In the original culture from the pleural cavity influenza-like forms were seen but could not be isolated. In the fifth case (767) a blood culture three days before death gave a growth of pneumococcus mucosus which was also grown from the lung at autopsy. Direct smear from the bronchus showed very few influenza-like forms. Our sixth negative finding was in a case of 20 days’ illness, the patient having had a recurrence (773). Staphylococcus pyogenes aureus, streptococcus viridans and B. xerosis were grown from the bronchus. Only a sarcina form grew from the lung, and a further probable air contamination occurred on the media from the cultures of the pleural cavity. The B. xerosis colonies were confusing, picked as possible B. influenzæ, and, before this was discovered, the overgrowth prevented further attempts to isolate the influenza bacilli. The last unsuccessful case was one with a general infection of a hemolytic streptococcus from an acute otitis media. The streptococcus was isolated from the bronchus, lung, spleen, arm vein and the middle ear at autopsy. It will be seen that in these seven negative cases technical difficulties prevented the isolation of the B. influenzæ, even if it had been present. I would not, therefore, conclude that the organisms were necessarily absent, but rather that we have failed either to secure material from the focus of infection or on account of the other reasons mentioned. It is very evident that a variety of secondary organisms very frequently overgrow the field and become numerically predominant. In our first case staphylococcus pyogenes aureus overgrew all the other organisms present in cultures from the lung material. B. influenzæ was, however, seen in the original 24-hour blood agar culture. It required 9 blood agar plates before the organism could be isolated. In another case 10 plates were used for the isolation.