Although it is well known that the influenza bacillus is the apparent etiologic agent in about 5 per cent of all cases of subacute bacterial endocarditis, comparatively few cases have been reported in which a hemolytic influenza bacillus was obtained from the blood cultures. This organism was first described in 1919, by Pritchett and Stillman,1 who observed it in material from the throats of normal persons and suggested the name Bacillus X.
A case of subacute bacterial endocarditis due to this organism in a 14 year old boy is presented, with the results of clinical, postmortem and bacteriologic studies. For the sake of comparison, some of the data are grouped in table 1 with those in seven similar cases previously reported. The organisms from two of the patients were only slightly hemolytic, but they were studied in such detail that it seems advantageous to include the cases.