This has been especially seen in pigeons in which it has been studied by Löffler, Cornil and Megnin, and Babes and Puscarin. Löffler found an ærobic, non-motile, non-liquefying bacillus in the false membranes, inflamed tissues, liver, lungs and blood, even in the leucocytes. It formed irregular masses, and grew in nutrient gelatine, blood serum and potato. It proved pathogenic to pigeons, linnets, rabbits and mice, but not to hens, Guinea-pigs, rats or dogs. Chickens, however, suffer from an acute diphtheritic affection caused by a nearly allied bacillus, and it remains to be seen whether the varying pathogenesis may not be due to the habit of long continued growth in a particular genus and an acquired unfitness for growing in the other. The pathogenesis is also different from the bacillus of diphtheria of man, and the two diseases are not usually inter-communicable, in spite of the fact that in rare instances infection has appeared to have taken place from man to birds. In pigeons and fowls the upper parts of the air passages and digestive tract are mainly involved, the tongue, fauces, corners of the mouth, nares, larynx, and conjunctiva. The bowels suffer less frequently and mostly concurrently with the mouth, nose and throat. The mucosa is deeply congested and in part covered by a yellowish exudate which may accumulate in masses, and dry into a firm substance. The disease affects particularly high bred birds, kept in close warm houses, and is often imported by prize animals returned from a show. There may be dullness, listlessness, sunken head, trailing wings and tail, erect plumage, diarrhœa, and, if the nose and throat are affected, a modification of the voice as in roup. Death may occur from asphyxia from the second to the fourth day near the beginning of an outbreak or the illness may last twenty days, after the more susceptible birds have been killed off. In investigating a series of outbreaks of roup in chickens in America, Dr. V. A. Moore found a non-motile bacillus allied to the colon bacillus which proved much more deadly to rabbits and guinea pigs than to chickens, and which was not found in the blood nor internal organs but only in the local lesions where inoculated. The disease tended to assume a chronic type in place of the acute form as seen in Europe. Three inoculated chickens escaped the disease altogether. It would appear therefore that we have here a disease distinct from that described by Lœffler, or that there was an absence of some unknown predisposing or contributing conditions that were present in the European outbreaks. In both diseases however infection is an undoubted factor and similar measures of prevention and even of treatment may be followed.