DIP1I TIIRRL'L 295 bacillus seems to be shorter than the diphtheria bacillus when grown upon blood-serum; that the cultures in bouillon seem to progress much more rapidly at a tem- perature of from 2o°~22° C. than those of the true bacillus; and that the pseudobacillus is not pathogenic for ani- mals. These slight distinctions are all exactly what should be expected of an organism whose virulence had been lost, and whose vegetative powers had been altered, by persistent manipulation or by unfavorable surround- ings. Park ! carefully studied this subject, and found that all bacilli with the exact morphology of the diphtheria bacillus, found in the human throat, are virulent Klebs- Loffier bacilli, while forms found in the throat closely resembling them, but more uniform in size and shape, shorter in length, and of more equal staining properties with Lofflefs alkaline methylene blue solution, can be, with reasonable safety, regarded as pseudocliphtheria bacilli, especially if it be found that they produce an alkaline rather than an acid reaction by their growth in bouillon. The pseuclodiphthcria bacilli were found in about i per cent of throats examined in New York; they seem to have no relationship to diphtheria. They are never virulent. A difference of possibly much greater importance is that observed by Martini,2 that the diphtheria bacillus will not grow in fluid antitoxic serum in which the pscudodiph- theria bacillus thrives. Both the real and the pseudoba- cilli flourish upon coagulated antitoxic serum. If this dif- ference in the behavior of the bacilli bears any relation to the so-called u specific immunity-react ionn of cholera and typhoid fever, it may he of great future importance. The diphtheria bacilli are always present in the throats of patients suffering from diphtheria, and constitute the element of contagion by being accidentally discharged by the nose or mouth by coughing, sneezing, vomiting, 1 Scientific Bulletin No. /, Health Department, City of New York, 1895. 2 CcntralbLf. Bakt. u. JParasitenk., Bd. xxi., No. 3, Jan, 30, 1897.