In =mice= subcutaneous injections proved fatal in five days with general dissemination of the bacillus. There are congested and hemorrhagic spots on the lungs, enlarged spleen, and the liver is marbled by numerous necrotic white masses, in the centre of which the capillaries are found to be blocked with the bacilli. This is so pathognomonic that Löffler looks on the inoculation of mice as the best means of diagnosis. Inoculated =rabbits= showed inflammation in the seat of inoculation and sometimes fibrinous peritonitis and enlarged spleen. Inoculation on the cornea produced a false membrane. In =Guinea pigs= induration and ulceration occurred in the seat of inoculation but recovery followed in 14 days. =Sparrows= inoculated in the pectoral muscles died in three days with yellowish necrotic tissue highly charged with bacilli. Inoculation of the =chicken= by Löffler and Megnin produced a circumscribed redness which soon disappeared. On the other hand Krajewski, Colin, Loir and Ducloux seem to have inoculated chickens successfully, and Cadeac says that the cultures are infecting for =sparrows=, =pigeons=, =turkeys=, =chickens= and =ducks=. It rests uncertain therefore whether the pseudomembranous pharyngitis of hens is a distinct disease as alleged by Löffler and Megnin or if the chickens used by these observers were not already immune by reason of a prior attack. Löffler’s experiments showed that _dogs_ and _rats_ were immune. Loir and Ducloux failed to infect cattle. In infected dove-cots a comparative immunity is attained by the older pigeons, which continue to harbor the germ, but do not suffer materially from its presence. They however communicate it to the susceptible young in the milky secretion produced in the crop and with which they feed them, and these accordingly perish in large numbers. Thus pigeons that are themselves in fine condition become the propagators of the bacillus to the more impressible. _Sparrows_ and other _small birds_ are also held to be common propagators of the germ, and if they too can secure an individual immunity and yet harbor the bacillus, their passage from yard to yard may be attended with great danger. The grains soiled by their bills and not swallowed are common media of transmission. Loir and Ducloux found the affection transmissible between man and pigeon. The identity of the bacillus with that of genuine diphtheria in man appears to have been thoroughly disproved by the observations of Roux and Yersin. The following differential characters have been noted: _Bacillus Diphtheriæ _Bacillus Diphtheriæ Columbarum_ (Klebs-Löffler)._ 1. In gelatine cultures grows only 1. In gelatine cultures grows at above 23°C. 15–17°C. 2. Kills Guinea-pig and dog. 2. Guinea-pig and dog nearly immune.