We quote from the preface: "It will be noted that the book deals with a discussion of the problem under consideration only in connection with those diseases of bacterial origin or which are due to the activity of a filtrable virus in the dissemination of which healthy human carriers are known to play a rôle; viz., carriers who either have never passed through an attack of the corresponding malady themselves, or, having done so, have clinically recovered. The maladies in question are cholera, diphtheria, typhoid and paratyphoid fever, dysentery, epidemic meningitis, poliomyelitis, pneumococcus pneumonia, certain streptococcus infections (such as camp septicemia, bronchopneumonia, septic sore throat, erysipelas and puerperal fever), influenza, and possibly also the pneumonic form of plague. Under these headings the various phases of the carrier problem have been discussed, i. e., the occurrence of active and passive carriers, the duration of the carrier state, the numerical relation between