II
These studies of mine of the respiration in sleeping and waking man make us understand more readily the signification of oppression during emotion. The difference is only one of intensity and degree, not of the nature and quality of the phenomenon. There is the same relation between waking and sleeping as between calm and agitation of mind. Let us consider the proof of this.
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.
Since I was in the laboratory at Leipzig I have made researches into the changes which cerebral activity exercises on the respiratory movements of men. This is a very complicated problem, as individual differences are great. In the curves which I obtained from some of my colleagues, who kindly placed themselves at my disposition for my observations on respiration, I found that the differences during intense mental work are very considerable. The reason for this must be sought in the variable excitability of the nerve-centres, and especially in the fact that the respiratory mechanism acts in a contrary manner during strong and during weak emotions. I made a few experiments on myself in order to see how the breathing changed, when someone suddenly made a great noise, as, for instance, by firing a gun behind my back while I was reading or absent-minded. I repeated these experiments on dogs, and always found that a deeper, often very deep, inspiration is caused, then there seems to be an arrest of respiration which may last for several seconds, the respiratory movements becoming immediately afterwards more frequent than before. Sometimes in a dog I observed that a shot caused, first, a deep inspiration, then a light expiration and inspiration, while the chest was much expanded; then another deep inspiration like the first, after which the chest emptied itself of the air accumulated in the lungs, and a succession of quicker breaths with more rapid inspirations than usual was drawn. Those who wish to find at once a plausible reason for all phenomena will perhaps say that these deep breaths serve to oxidise and vivify the blood streaming through the lungs, so that in this way the organism may prepare itself for defence.