_Causes._ This affection is more common in this class of animals than in the herbivora, being apparently dependent in great part on their artificial habits of life, the sweet and stimulating diet and the derangement of the digestive organs. The lowering of the general health in connection with privation or disease and especially canine distemper, rachitism or indigestion must be recognized as predisposing causes, while the accumulation of tartar on the teeth, or the decay of the teeth themselves, constitutes a potent exciting local cause. In connection with such cretaceous deposits the decomposing elements of the food collect, and the irritant products of their fermentation lead to disease of the gums, congestion and ulceration. Superadded to this is the bacteridian infection of such diseased parts, through which the ulceration is started, maintained and extended. This infection is not that of a specific microbe, but usually of a multiplicity of germs, one or more of the bacteria that live habitually in the healthy mouth, taking the occasion of the existence of a wound, or of a reduction of vitality to colonize the mucosa which would otherwise have remained sound. The microbes actually found in the ulcers are very varied. Pasteur isolated a spirillum, Fiocca the bacillus salivarius septicus, others have found pus bacilli, and in sucking kittens the bacillus coli communis. But the attempts made to convey the disease to healthy mouths by the transfer of the microbes have usually failed (Pasteur, Netter, Cadeac). To establish their pathogenic action therefore, it appears to be necessary to furnish a susceptible mucosa as well as an infecting microbe. This explains why the disease does not spread as an infection, the average mouth is immune and it is only when it becomes the seat of a wound, bruise or other injury, or when the general system has become so reduced that the resisting power is a minor quantity, that the hitherto harmless germ becomes actually pathogenic.