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.
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.
Fig. 6.—Alteration of the Cardiac Pulsation through Emotion
After we had assured ourselves that these alterations of the pulse were much less marked after other noises which did not resemble the loading of a gun, we wished to convince ourselves whether the agitation was caused by a fear of weapons. The next day the dog was again brought into the laboratory, and while he lay on the table, and the action of the heart was being marked, someone walked past him with a gun on his shoulder. The dog recognised it again, became restless, tried to rise, his heart beat violently, he began to wag his tail, and followed the hunter with satisfied glances.