F. H. Pike

The rôle of afferent impulses in the control of respiratory movements

As the result of further experimentation, we wish to add to a previous statement (American Journal of Physiology, 1917, XLII, p. 395) the following facts: 1. The movements of the ribs, which cease after division of the dorsal roots of the spinal nerves in the thoracic and cervical regions, are resumed when the phrenics are divided. 2. The respiratory movements become labored when the vagi are divided in the neck after these procedures, and soon cease. The effects of vagotomy are more severe if the dorsal roots of the cervical nerves have been included in the section than if the thoracic nerves alone are affected. 3. The results of combined section of the dorsal roots of the spinal nerves and the vagi are similar to the effects of combined section of the brain stem below the corpora quadrigemina and the vagi. Transection below the corpora quadrigemina adds little or not at all to the severity of the effects following section of the dorsal roots. 4. Costal respiratory movements are resumed after section of dorsal roots, brain stem below the corpora quadrigemina and phrenics if the vagi are intact. We believe that these experiments bring the intercostal muscles into line with the other skeletal muscles so far as the functional relations of afferent to efferent spinal nerve roots are concerned. 1 We believe also that the experiments show that it is necessary that afferent impulses shall not merely have access to the central system, but that they shall go to a particular part of the central system in order to fulfill their function. In the case of the respiratory movements, afferent impulses from the intercostal muscles must go as far up as the corpora quadrigemina. The medulla oblongata seems sufficient for the establishment of any necessary connection of the vagi with efferent paths to the respiratory muscles.

Contracture of the Rectus Abdominis, Tetany, Calcium and Phosphorus, after Spinal Transection, with and without Thyro-parathyroidectomy

As one phase of some observations on the effects of parathyroidectomy on cats, 1 a previous study 2 showed that on stimulation of the rectus abdominis muscle following thyroparathyroidectomy, more contracture usually appeared than was the case with the same muscle stimulated in the same manner in control animals. During the past months a series of experiments has been done on 20 cats in which the ionizable calcium and inorganic phosphorus of the blood were determined from 2 to 3 days after (1) aseptic transection of the spinal cord alone in the upper thoracic region and (2) when thyroparathyroidectomy was done at the same time as the spinal transection. The working power of the curarized muscle, together with the presence or absence of tetany and of contracture, was determined in the same manner as in previous experiments. The results are given in Table I. It appears from the table that 1. Either contracture or tetany was present in all but one case, in which the contracture occurred at the beginning of the excitation of the muscle and was merely transitory. 2. Contracture and tetany were found together in only 6 of the 20 experiments. There appears to be no necessary relationship between them. 3. Contracture did not occur when the ratio of calcium to phosphorus was less than one, except in one case (No. 9). From these and previous observations it would appear that contracture occurs infrequently when the ratio of calcium to phosphorus is less than one, and then only when the calcium is relatively low; on the other hand, contracture was observed in only one case where the concentration of phosphorus was above 8 mg. per 100 cc. serum. (No. 6.)

The effect on blood pressure of removal of portions of the spinal cord in the thoracic region

The argument for the functional independence of the peripheral ganglia of the sympathetic nervous system has rested largely on the experiments of Goltz, who removed portions of the thoracic region of the spinal cord after previous transection. Two conditions should be sharply distinguished here: (1) when the transection of the spinal cord is in the lower cervical region above the level of outflow of the sympathetic fibers from the thoracic roots. This condition has been considered by Sherrington, 1 who showed that the blood pressure fell markedly on actual destruction of the spinal cord 300 days after the first transection. (2) When the spinal cord is transected in the upper thoracic region, leaving a functional connection of the medulla oblongata with the periphery through a few rami communicantes of the sympathetic system emerging with the roots of the upper thoracic nerves. Miss Yates 2 showed that systemic blood pressure fell on paralysis of the medulla oblongata some days after the transection of the spinal cord. It remains to determine the actual effect upon systemic blood pressure of removal of portions of the spinal cord below the level of transection after an interval of recovery. Cats were used in our experiments. The spinal cord was transected under aseptic conditions at varying levels from the second to the ninth thoracic, and the animal allowed to recoyel. Some days afterward, the animal was again anesthetized and the systemic blood pressilre recorded from a cannula in one carotid artery. A mercury manometer was used. In one cal, in which the level of transection was just below the fifth thoracic root, the mean level of blood pressure was 114 millimeters of mercury six days after the transection. The blood pressure remained at 78 millimeters after removal of a section of the spinal cord eight centimeters long below the level of the first transection.

The postural activity of the rectus abdominis muscle of the cat

If we accept Sherringtons 1 view that a muscle may undergo changes in length without concomitant changes in tension as a means of preserving a certain posture or attitude of the body, we find that the rectus abdominis of the cat manifests this property in a high degree. The animals used for experiment were etherized and a tracheal cannula inserted. The skin was incised in the median line of the thorax. The pectoral muscles of one side were then severed close to their attachments to the sternum and sternal portions of the ribs and reflected outward. The tendinous insertions of the rectus abdominis on the ribs were divided and the free upper end lifted out. A thread was tied about the tendinous end of the muscle and led through a system of small pulleys to a muscle lever. The abdominal wall was kept intact. A rise of the writing point of the lever indicated a shortening of the muscle, while the writing point fell when the muscle relaxed. The thoracic and abdominal respiratory movements were recorded by Verdin tambours connected to Crile stethographs. Small changes in the length of the rectus abdominis occurred during ordinary respiration. But if fluid, usually an M/8 solution of sodium chloride, was introduced into the stomach through a stomach tube passed down the esophagus, or directly into the peritoneal cavity through a hypodermic needle, the muscle promptly relaxed, the amount of relaxation being proportional to the amount of fluid introduced, and continuing until the limit of distension of the abdominal cavity was reached. This limit of distension is determined by the muscular wall and not by the skin. The relaxation occurs when fluid flows in at pressures of only two or three centimeters of salt solution, and a contraction occurs when fluid is flowing out of the stomach.