The designation of the miscellaneous group of pneumococci as type IV has led to considerable misconception as to the real nature of these micro-organisms. It is difficult for those who are not intimate with this classification to realize that the so-called type IV is not a specific type in the sense that the three fixed types are specific, but that it is merely a term used to cover all the remaining strains that do not fall into types I, II or III. It has long been known that type IV pneumococci were amenable to further and more accurate classification; indeed, several observers (Olmstead,1 Clough2 and Robinson3) have conducted investigations along this line.
In a recently published article, Cooper, Edwards and Rosenstein,4 who were working in the general investigation of pneumonia under the direction of Dr. Park, have reported ten distinct immunologic types obtained from the group