A BIOLOGIC CLASSIFICATION OF PNEUMOCOCCI BY MEANS OF IMMUNITY REACTIONS

The early work of Koch on etiology led him to formulate certain laws which he demanded should be fulfilled before the relationship of any micro-organism to disease could be regarded as satisfactorily established. Subsequent students have sought to fulfil the requirements of Koch, and the result has been that with the elucidation of each well-recognized infection, a single bacteriologic unit has become accepted as the causative agent. Bacteria, however, are not strictly limited in the pathologic process which they induce, and the lesion caused by a single variety may vary somewhat with its location in the animal body. The pathologic and clinical study of disease is, however, so extensive to-day that the various types of activity of the same bacterial race have been thoroughly described and correlated, so that the nature of the infectious agent can in most instances be assumed from the character of the pathologic process. From the