While the animal was perfectly quiet I motioned to my servant to fire a gun, but he failed. It was an old hunting-gun, badly loaded perhaps, and only the cartridge had caught fire. The dog, however, at once tried to rise, and became strangely excited, much to our surprise. I had my hands on the instrument which lay on the ribs where the heart beats, and felt that its palpitations had become stronger and more rapid. About a minute later we succeeded in taking the curve _B_ in fig. 4, from which may be seen how much more frequent the pulsations were. The animal had become so restless that we had to give up the experiment and set him at liberty. When he was on the ground he went round the laboratory sniffing everywhere. Presently we took the curve _C_, fig. 4, from which we can see that the emotion was not yet over, since the beating of the heart is still quicker than in the normal curve marked in fig. 3. [Illustration: _T_ _C_ _B_ FIG. 4.--CARDIAC PULSATION DURING EMOTION] There were several of us together when this experiment was made--the students of the laboratory, my assistants, and Professor Corona, and we were all astonished at what took place. Some of the bystanders said at once that it must be a hound. We had always taken him for a watch-dog, as he was very big, and did not look in the least like a hound. We determined to try a decisive experiment the next day. We waited till the animal was perfectly quiet, and then held a gun so that he could see it at a distance of a few steps from him, without threatening him in any way. The dog at once recognised the weapon, and again grew excited, showing a considerable change in the cardiac curve. [Illustration: _D_ _T_ FIG. 5.--NORMAL CARDIAC PULSATION] But the most evident proof that it was a hound was given by the very violent emotion and the unexpected excitement which took possession of him as soon as he heard the noise caused by the loading of the gun and the click of the trigger. Even when he saw nothing, and this noise was made at some distance from him, the beating of the heart changed instantly (as may be seen in the following curve), and the animal tried to rise and sniffed the air. The curve _D_, fig. 5, shows the pulsations written with the cardiograph applied to the thorax of the animal when quiet. At a given time I signed to a person, whom the dog could not see, to load the gun. Scarcely had the animal heard the clicking than he moved; a few seconds passed, during which it was impossible to take the curve, the dog being so restless. About a minute later I succeeded in obtaining the curve _E_, fig. 6, in which one can see that the form of respiration, as well as the frequency and force of the cardiac pulsations, is altered. [Illustration: _E_ _T_ FIG. 6.--ALTERATION OF THE CARDIAC PULSATION THROUGH EMOTION]