The immediate cause of the rupture of the valve of the heart had evidently been an increase of circulation, brought on by an increase of exercise; but the remote cause consisted in the remarkable thinness of the walls of the valve of the heart. This case is remarkable in more than one respect; first, because examples of rupture of the valve of the heart are very rare; and, secondly, because this rupture had its seat in the left valve of the heart, while, usually, in both the human being and the quadruped, it takes place in the right; and this, without doubt, because the walls and the valves of the right side are thinner. Diseases of the investing membrane of the lungs, and the pleura of the thoracic cavity, and of the substance of the lungs, are more frequent than those of the heart. PLEURISY, or inflammation of the membrane of the chest and the lungs of the dog, is not unfrequent. There are few instances of inflammation of the lungs, or pneumonia, that do not ultimately become connected with or terminate in pleurisy. The tenderness of the sides, the curious twitching that is observed, the obstinate sitting up, and the presence of a short, suppressed, painful cough, which the dog bears with strange impatience, are the symptoms that principally distinguish it from pneumonia. The exploration of the chest by auscultation gives a true picture of it in pleurisy; and, by placing the dog alternately on his chest, his back, or his side, we can readily ascertain the extent to which effusion exists in the thoracic cavity; and, if we think proper, we can get rid of the fluid. It is not a dangerous thing to attempt, although it is very problematical whether much advantage would accrue from the operation. With a favourite dog it may, however, be tried; and, to prevent all accidents, a veterinary surgeon should be entrusted with the case. PNEUMONIA, or inflammation of the substance of the lungs, is a complaint of frequent occurrence in the dog, and is singularly marked. The extended head, the protruded tongue, the anxious, bloodshot eye, the painful heaving of the hot breath, the obstinacy with which the animal sits up hour after hour until his feet slip from under him, and the eye closes, and the head droops, through extreme fatigue, yet in a moment being roused again by the feeling of instant suffocation, are symptoms that cannot be mistaken. Here, from the comparative thinness of the integument and the parietes, we have the progress of the disease brought completely under our view. The exploration of the chest of the dog by auscultation is a beautiful as well as wonderful thing. It at least exhibits to us the actual state of the lungs, if it does not always enable us to arrest the impending evil.