The first series of experiments upon the abdominal viscera were performed upon animals. The abdominal wall was opened under anesthesia. The viscera were exposed to examination with as little manipulation as possible. The condition of peristalsis and the size of the blood vessels was carefully noted. The fingers of the observers were placed upon different areas of the back and neck in part of the experiments, and in others the muscles also were exposed to view. For the first series, electricity was used except where other forms of stimulation are mentioned. The stimulation of the peritoneal coat, or the muscles, or the inner wall of the cardiac end of the stomach was followed by the contraction of the muscles near the sixth to the eighth thoracic spines. The inner walls of the stomach were stimulated by pricking and by the use of a hot glass rod. The reflex muscular contractions followed as in the case of the electrical stimulation. The stimulation of the peritoneum and the gastric muscles by pricking, etc., did not initiate the contractions so constantly. The area of reflex muscular contractions varied somewhat in different animals, but remained constant for each animal, at least during its life under anesthesia. Electrical stimulation of the pyloric end of the stomach gave rise to contraction of the spinal muscles from the seventh to the tenth, but usually near the ninth thoracic spine. This corresponds to the eighth in the human being. In all these experiments, the cervical muscles were somewhat contracted. We did not determine what individual muscles were involved in the reaction. The stimulation of the duodenum, pancreas and gall-bladder caused the contraction of the muscles near the tenth and eleventh thoracic spines. (It must be noted that cats and dogs rejoice in the possession of one or two extra thoracic vertebrae.) The stimulation of the rectum was followed by contractions of the muscles near the lumbo-sacral articulation. The stimulation of the portions of the intestine between the duodenum and rectum caused muscular contractions which were fairly equally divided between the tenth thoracic spine and the lumbo-sacral articulation. The stimulation of the caecum and appendix caused the reflex muscular contractions to appear near the fourteenth thoracic and the first lumbar spines. The interior of the appendix was stimulated by pricking, and the reflex contractions appeared as before. The electrical stimulation of the kidneys and the supra-renals caused the contraction of the muscles near the fourteenth thoracic spine, sometimes the contractions appeared near the twelfth and thirteenth. These correspond to the eleventh and twelfth in man. The electrical stimulation of the small intestines was very efficient in producing the reflex contractions. The neighborhood of the caecum was especially sensitive to any stimulation. Reflex movements were very easily initiated from this region by slight stimulation. The colon, on the other hand, was not apt to give rise to the reflexes unless the stimulation was very strong. Prickings, etc., of the inner wall had almost no effect in producing the reflex muscular contractions. The peritoneum over the intestines seemed to be of about the same sensitiveness throughout, so far as we were able to determine. So far as the initiation of reflex muscular contractions can be considered a criterion, the caecal region is the most sensitive part of the intestines, the duodenum is next in order, the other parts of the small intestine about alike, and the colon is least sensitive of all. The rectum is even more sensitive than the caecal region in its very lower portion, near the anus, but the upper part of the rectum is not more sensitive than the colon. Stimulation of the anal tissues caused very intense contractions of the sacral muscles, and usually of the leg muscles also. The stimulation of the anal tissues, and sometimes those of the caecal region caused the contraction of the cervical muscles also. In some cases, the stimulation of the kidneys and supra-renals caused the contraction of the cervical muscles, but this reaction was not constant.
The centers thus suggested were then used for further work in the determination of the somato-visceral reflexes. Stimulating manipulations were given to the tissues near the sixth and seventh thoracic vertebrae. Gastric peristalsis and secretion were found to be increased after a latent period of about five minutes. Soon after, the peristaltic waves appeared in the walls of the intestines. At the same time, the viscera were found to be lighter in color. By the use of a reading glass, the constriction of the small arterioles was very apparent. The blood pressure seemed to be raised, judging by the character of the heart beat, though it was not measured in any of the animals. A slight rise in temperature was perceptible to the touch, though the intestines were exposed to the air and no effort was made to conserve the heat. It was not possible, under the conditions of our experiments, to affect the secretion and movement of one part of the stomach rather than another, nor to affect the stomach to the exclusion of the duodenum. The stomach center may then be located in the sixth to the eighth thoracic segments of the cord. The artificial lesion in this area was followed by a relaxation of the walls of the stomach, a dilatation of its vessels, and its distension with gas. The duodenum was always affected to some extent by anything which affected the stomach. Stimulating manipulations of the tissues near the eighth to the tenth thoracic vertebrae caused contractions of the blood vessels of the pancreas. The effects upon the pancreatic secretion were not studied. Stimulating manipulations of the tissues in the neighborhood of the tenth to the fourteenth vertebrae was followed by increased peristalsis of the duodenum and small intestines, and by characteristic vascular changes. The walls of the viscera became lighter in color, and the arterioles were contracted, as seen with the realing glass. The blood pressure was greatly increased, as was evident from the character of the pulse changes. Artificial lesions in the same area produced conspicuous effects. The vessels became dilated, and the color of the blood within them became darker and more of a purple hue, as if it were more nearly venous than before. Blood pressure was decreased. The visceral walls were relaxed, and the intestines became distended with gas.
The gas found in these cases was set free by the blood. The amount of gas which can be carried in a solution varies with the pressure and temperature of the solution. The temperature of the body remains fairly constant, and can be disregarded. Blood under high pressure can carry a certain amount of carbon dioxid in solution. If the pressure of the blood in the vessels is decreased, the blood is not able to dissolve so much of the gas, and it is therefore set free wherever the pressure is lowest. Under the conditions of our experiment the gas could not have been due to fermentation. In the case of persons who suffer from flatulence it is probable that part of the gas, at any rate, is due to fermentation. The tests made to determine the origin of the gas in the experimental cases were as follows: The intestines were exposed to view as before, and their condition noted. Large, soft cords were then tied around the intestines at intervals. The ligatures were carefully placed to avoid the large blood vessels and nerves. The mesentery was merely punctured. The cords were tied tight enough to prevent the passage of gas from one division to another. The intestines were cut in some places. No gas escaped, hence the gas was not present in the intestines at the beginning of the experiment. The artificial lesion was produced, or, in some cases, inhibition was given, in the region of the eighth to the twelfth thoracic vertebrae. All of the intestinal vessels were dilated, the blood pressure became lowered, and the uninjured areas of the intestines between the ligatures became distended with gas. Puncture of some of these areas permitted the escape of an almost odorless gas, which we supposed to be chiefly carbon dioxid. Gas was often eliminated by way of the anus at these times. Other sections of the intestines whose walls between the ligatures were still intact remained distended with gas for some time. After the artificial lesion was removed, the blood vessels and the intestinal walls returned to their normal condition very slowly, and the gas disappeared. Puncture of these sections of the intestines was not then followed by the escape of gas. The artificial lesion, then, caused congestion of the intestinal tract, lowered blood pressure, and the accumulation of gas in the intestines. The possibility of an accumulation of gas in the peritoneal cavity is being investigated. The absorption of the gas after stimulation of the splanchnic area must have been by way of the blood or lymph to the lungs, for there was no other pathway of escape for it. (Note A.) The return to the normal appearance after the pressure was removed was very slow, indeed, if the artificial lesion had been maintained for a long enough time for the effects to become pronounced. Subsequent stimulation of the tissues in the same area hastened the return to the normal appearance of the vessels, but was sometimes followed by reversed peristalsis. Direct stimulation of the splanchnic nerves by electricity or by pricking the nerve trunk caused lessened peristalsis, under the conditions of our experiments, and dilatation of the the splanchnic vessels. No explanation is offered of this apparent paradox, but the facts are as stated. The phenomena were so often observed upon so many animals that it is not possible to suppose that some individual peculiarity is responsible for the condition. The walls of the spleen became roughened by direct stimulation of its nerves, and also by the stimulation of the tissues near the eleventh thoracic vertebra. This reaction was possible only during the later stages of digestion.
Stimulating manipulations of the tissues near the thirteenth and fourteenth thoracic spines was followed by rather striking changes in the activity of the supra-renal capsules. Their blood vessels became dilated very conspicuously. At the same time the blood vessels of the intestines, stomach, pancreas, spleen, heart and lungs, the conjunctivae, and the mucous membranes of the mouth and nasal passages became greatly constricted. The pulse showed very high blood pressure. The blood vessels of the limbs and of the brain did not display such conspicuous effects. In some animals these vessels seemed to be affected by the activity of the supra-renals, and in others no effects whatever were visible. In the cases where the changes did appear, the dilatation may have been due to the increased blood pressure. The internal secretion of the supra-renals is supposed by some investigators to affect only the muscles of the blood vessels which are supplied with vaso-constrictors from the sympathetic ganglia. The limb muscles are poorly supplied with constriction, and the constrictors of the brain have not yet been absolutely demonstrated. Our experiments do not yet throw any light upon these questions, and further investigations are in progress. The
artificial lesion in the same area was followed by increased caliber of
the intestinal vessels and low blood pressure, but we were not able to
demonstrate any effect upon the vascular system which was beyond question
due to the action upon the supra-renals of the artificial lesion in the
center controlling these glands.
The vagus nerves were sectioned in another series of experiments. The results already described were usually intensified in the animals subject to this mutilation. The direct stimulation of the splanchnic nerves by pinching, pricking or electricity initiated reversed peristalsis. This was so pronounced that in some cases bile was quietly ejected from the mouth. Bile was found in the stomach in every case in which direct stimulation of the splanchnic nerves followed section of both vagi. No active vomiting occurred after section of the vagus. In nearly every instance, direct stimulation of the intestinal or gastric walls initiated reversed peristalsis. Stimulating manipulations of the splanchnic area also caused reversed peristalsis in many instances, though not in every animal subjected to the experiment. When both vagi were cut, the stimulation of the central end of either or both produced so visible effects upon the viscera. It seems that sensory impulses carried upward through the vagus nerves do not affect the activity of the splanchnics to any great extent, if at all. After the section of only one vagus, the stimulation of its central end caused very pronounced increase in the gastric movements. The impulses were evidently carried upward to the center in the medulla and downward by way of the intact nerve of the other side. The relation between the right and left vagus is, therefore, very close. When both vagi were cut, the stimulation of the central end of either or both produced so visible effects upon the viscera. It seems that sensory impulses carried upward through the vagus nerves do not affect the activity of the splanchnics to any great extent, if at all. After the section of only one vagus, the stimulation of its central end caused very pronounced increase in the gastric movements. The impulses were evidently carried upward to the center in the medulla and downward by way of the intact nerve of the other side. The relation between the right and left vagus is, therefore, very close. The nausea that accompanies a “stiff neck” may perhaps be referred to the effects of the abnormal pressure of the contracted muscles upon the vagus. The nausea and the vomiting of bile that annoys many of those “who do down to the sea in ships” may be referred to the irritation of the center for the vagus in the medulla by the excessive stimulation of the vestibular nerve, whose sensory nucleus is so closely associated with that of the vagus. The excessive stimulation of the vagus center exhausts its neurons, and the effect is similar to the experimental section of the nerve. The vagus is sensory to various organs. If these are not normal, the liminal value of the vagus center is abnormally low, and is therefore easily affected by the abnormal stimulation from the center for the vestibular portion of the eighth nerve. If the organs from which the vagus carries sensory impulses are fairly normal, the center is able to maintain fairly normal metabolism for some time in the presence of the excessive vestibular impulses. Hence, the best preventive of seasickness is found in a normal condition of the area of sensory distribution of the vagus nerves. Variations in susceptibility are caused by variations in the liminal value of the nerve centers, by variations in the irritability of the vestibular nerve endings, and by variations in the structural relations of the nerve centers.
In another series of experiments, the sympathetic ganglia were removed. None of the reactions involving the spinal muscles were to be secured under any circumstances. The possibility of the passage of impulses through the sympathetic system alone was tested by a very exhaustive series of experiments upon many animals. The spinal nerves were sectioned all along the splanchnic area. No reflex effects were to be secured, either visceral or somatic. The most instructive tests were made upon peristaltic movements. Peristalsis is carried from one part of the intestinal walls to another from muscle to muscle if the nerves are cut or paralyzed by any of the poisons used for the purpose. If the intestine is sectioned the peristaltic waves stop at the section, when the nerves are cut, but pass over the section if the nerves are intact. If the nerves from the semilunar ganglion are cut, peristalsis stops at the section of the intestine. If the sympathetic ganglia are extirpated, the peristaltic waves stop at the section. Destruction of the spinal cord at the level of the origin of the white rami in relation with the intestines prevents the passage of the peristaltic wave over the intestinal section. It was thought that the shock of the destruction of the cord might account for the fact that the peristaltic wave was unable to cross the section. The upper dorsal and the lumbar portions of the cord were destroyed and the splanchnic portion left intact. All the other nerves also were intact. The stimulation of the intestine above the section caused peristalsis which crossed the section as if the reflex arc were normal. Hence, the shock to the nervous system could not account for the phenomena observed. Other tests were made to eliminate the possibility of error in the interpretation of the results. The series indicates that the chief, if not the only, path of reflex action involving the visceral muscles and glands passes through the spinal cord or the centers in the floor of the fourth ventricle and acqueduct of Sylvius. Reflex effects of one viscus upon another are carried by way of the cerebro-spinal system. The sensory nerves carried with the sympathetic nerves originate in the sensory ganglia in the intervertebral foramina. They are thus enabled to affect the spinal muscles. The impulses which affect the viscera originate in the lateral horns of the spinal cord. The impulses from the cerebro-spinal sensory nerves are thus able to affect viscera. It is by means of this relation that bony lesions affect visceral action. NOTE A.—In surgical operations the experiments performed upon animals are practically duplicated upon human beings. It has been found that during the operation under the surgical anesthesia the reflex muscular contractions occur in persons as in lower animals. The muscular contractions so produced, may, if they are permitted to remain present, be a cause of evil after affects. The inhibition exercised by contractions along the lower dorsal and lumbar regions may be a cause of post operative meteorism. This view of post operative meteorism was taken by Dr. Maria S. Wing, of Los Angeles. An extract from a letter reporting her success is given here with her permission: “On my arrival at the hospital I found the patient suffering greatly, with face drawn and anxious, sleepless, fast losing her strength and grip. The gas distended all the soft parts from the sternum to the pubic bone into one immense tumor, and the faithful nurses, under the guidance of an able, resourceful and experienced sister, had worked over her night and day without any improvement. Gas is, as they so often have seen, the great danger in abdominal surgery, and they have so often found their efforts inadequate. They had little hope for this case. “I put my hand under her back and found the muscles very tense. Nor did they easily relax, but I kept up the manipulations until she told me with a moan that she was tired. By this time the muscles were fairly well relaxed, and I ordered a hot water bottle at her back. But the distention was so unchanged and I began to feel discouraged. Then, in less than five minutes, she exclaimed in horror: “Has the wound opened and let out the gas? It is gone!” “And gone it was, without any escape by mouth or rectum. The abdomen was entirely collapsed. I had to explain to her how the blood was not carrying the gas to the lungs, that she would not have had any gas in case the blood had not been stagnant and that now all trouble was over. She sank into a deep, peaceful sleep that lasted until the next morning, and she has had neither pain nor other difficulties since then. Each time any sign of gas has appeared I have been sent for, and the relief is always immediate.” The patient referred to by Dr. Wing had suffered total hysterectomy. The incident described in the letter occurred upon the fifth day. The meteorism had prevented sleep from the time of the operation until the relief given by Dr. Wing. The experience has been duplicated since that time by Dr. Wing and by others. NOTE B.—The following experiments were performed upon cats and white rats in order to determine whether gas might accumulate in the peritoneal cavity. Five animals were used. The animals were anesthetized, the abdomen was opened under warm water, and the artificial lesion produced in the splanchnic area. Small bubbles of gas appeared upon the mesentery and omentum, became larger, and arose to the surface of the water. Gas appeared within the omental sac. |