Figure 6.—Failure of the cava blood (added at a) to produce inhibition when excitement has occurred after removal of the adrenal glands. The muscle later proved sensitive to adrenin in blood in the ratio 1:1,000,000.
(3) As already shown, sometimes the effect produced by the “excited” blood was prompt inhibition, sometimes the inhibition followed only after several beats, and sometimes a slowing and shortening of contractions, with a lower tone, were the sole signs of the action of adrenin. All these degrees of relaxation can be duplicated by adding to inactive blood varying amounts of adrenin. [Fig. 7] shows the effects, on a somewhat insensitive muscle preparation, of adding adrenin, 1:1,000,000 (A), 1:2,000,000 (B), and 1:3,000,000 (C), to different samples of blood previously without inhibitory influence. These effects of adrenin and the effects produced by blood taken near the opening of the adrenal veins are strikingly analogous.
Figure 7.—Effect of adding adrenin 1:1,000,000 (A), 1:2,000,000 (B), and 1:3,000,000 (C), to formerly inactive blood. In each case a marks the moment when the quiet blood was removed, and b, the time when the blood with adrenin was added.
(4) Embden and v. Furth[1] have reported that 0.1 gram of suprarenin chloride disappears almost completely in two hours if added to 200 cubic centimeters of defibrinated beef blood, and the mixture constantly aerated at body temperature. “Excited” blood which produces inhibition loses that power on standing in the cold for twenty-four hours, or on being kept warm and agitated with bubbling oxygen. This change is illustrated in [Fig. 8]; the power of the “excited” blood to inhibit the contractions of the intestinal muscle when record A was written was destroyed after three hours of exposure to bubbling oxygen, as shown by record B. The destruction of adrenin and the disappearance of the effect which adrenin would produce are thus closely parallel.
Figure 8.—The effect of bubbling oxygen through active blood. A, relaxation after active blood applied at a; B, failure of relaxation when the same blood, oxygenated three hours, was applied to a fresh strip at b.
All these considerations, taken with the proof that sympathetic impulses increase secretion of the adrenal glands, and taken also with the evidence that, during such emotional excitement as was employed in these experiments, signs of sympathetic discharges appeared throughout the animal from the dilated pupil of the eye to the standing hairs of the tail-tip, led us to the conclusions that the characteristic action of adrenin on intestinal muscle was in fact, in our experiments, due to secretion of the adrenal glands, and that that secretion is increased in great emotion.
The Evidence that Adrenal Secretion is Increased by “Painful” Stimulation
As mentioned in the first chapter, stimulation of sensory fibres in one of the larger nerve trunks is known to result in such nervous discharges along sympathetic paths as to produce marked inhibition of digestive processes. Other manifestations of sympathetic innervations—e. g., contraction of arterioles, dilation of pupils, erection of hairs—are also demonstrable. And since the adrenal glands are stimulated to activity by sympathetic impulses, it was possible that they would be affected as are other structures supplied with sympathetic fibres, and that they would secrete in greater abundance when sensory nerves were irritated.