If we wish to study the respiratory movements with great accuracy, it is no longer sufficient to observe how the thorax expands and contracts; we must apply to chest and abdomen extremely delicate instruments which mark automatically the slightest motion of the thorax. These instruments, called _pneumographs_, are made in such a manner as to cause no annoyance to the person on whom they are applied. I shall communicate a few observations which I made on my dog. He is such a good animal, that when I apply the pneumograph to the thorax and put him on the table in order to write the respiratory movements, he lies for hours quietly slumbering. But a mere nothing, the slightest noise, is sufficient to cause an alteration in the rhythm of breathing. This is an experiment which I have often repeated before my colleagues, in order to show the extreme sensibility of the respiratory mechanism to psychic conditions. While all was quiet and the pneumograph was writing the respiratory curve, it was enough if I spoke to someone, if I gave an order, touched the apparatus or the table, or even if I looked at the dog and spoke kindly to him--his breathing immediately became more rapid. If the impression were slight, the effect lasted a few seconds; sometimes I found that a single respiration had become quicker, but generally the effect lasted longer. If a person whom the dog did not know placed himself before him, the former respiratory rhythm did not return; if I scolded him, the effect lasted many minutes till the emotion had subsided.