In the preceding paper (1) observations on the nature of the soluble specific substance of pneumococcus have been recorded. The present work concerns itself with the facts thus far ascertained in a comparative study of the chemical and immunological reactions of the protein 1 of pneumococcus. It seemed of interest to study the immunological relationship of the bacterial protein to the soluble specific substance of pneumococcus, and in the present paper certain differences in the serological

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... ificity of the two classes of substances are brought out and related to their chemical nature. It would be beyond the scope of the present paper to attempt a review of the extensive literature on the subject of bacterial nucleoproteins in general, and this has already been done in reference books (2). This work is presented, despite its incompleteness, because it points the way to a comparative study of the immunochemical relations existing between two different cellular constituents of the same organism. The first of these components, the so called soluble specific substance, has been discussed in the preceding paper; it need only be pointed out here that this reactive substance possesses none of the chemical properties of protein, that although antigenically it appears capable of stimulating little or no antibody response, serologically it exhibits to an extraordinary degree the reactions of type specificity in antipneumococcus sera. In other words, this non-protein constituent in isolated form is relatively and perhaps x The word protein as used in this paper refers only to that portion of the dissolved pneumococcus cell precipitable in the cold by acetic acid and consisting mainly of nucleoprotein and mueoid.