REPORT OF SOME OBSERVATIONS UPON THE FORM WM. H. HOWELL, A. B., AND F. DONALDSON, JR., A. B. (Biological Laboratory of the Johns Hopkins University). In the course of some experiments which we are making upon the isolated mammalian heart, a dog, evidently suffering from some form of heart disease, came under our notice. We supposed that either the mitral or aortic valves were diseased, and Professor Martin suggested that it would be of some interest to take tracings of the arterial pressure and the form of the pulse-wave. It was especially desirable to know the arterial pressure, since such an observation could not be made upon the human subject except in a very indirect way. A post-mortem examination which Dr. Tiffany was kind enough to make for us, revealed the fact that there was a patent ductus arteriosus, establishing a very wide communication between the aorta and the pulmonary artery. There was also apparently some slight insufficiency of the mitral and the pulmonary valves. The aorta from its origin to the bend was considerably dilated, though there was no evidence of any atheromatous changes in the walls of the artery. The heart weighed 97 grams, and, upon comparison with the hearts of other dogs of about the same weight, from fifteen to eighteen pounds, showed general enlargement, together with some hypertrophy of the walls of the left ventricle. The heart of a dog of about the same weight, from which tracings were taken for comparison, weighed 66.5 grams. At the opening of the ductus arteriosus into the aorta there was a small valvular fold, not nearly large enough to cover the opening, but so placed as to direct the stream of arterialized blood sent out from the left ventricle at each systole, along the aorta, and prevent it from passing into the pulmonary circulation, acting apparently in somewhat the same way as the Eustachian valve in the foetal heart. After the completion of the systole, however, when the elastic recoil of the aorta had set in, this valve could have offered no obstacle to the passage of blood from the aorta into the pulmonary artery, indeed would rather have guided any backward current in that direction. This form of heart disease is so rare that it was thought best to make a short report of it before this Faculty, in order that the facts observed might be placed upon record. The only recorded case that we have been able to find is the one reported by Dr. Hilton Fagge in the Guy's Hospital Reports, 1873. As we were not competent to make a satisfactory auscultation of the case, we requested Dr. Donaldson to examine the dog for us. This he very kindly consented to do, and gave us the following written report of the symptoms observed: 'I carefully auscultated the dog, and found the heart beating at about 140 per minute; the impulse, as compared with that of a healthy dog, was much increased; the apex of the heart extended much further to the left of the sternum, showing marked hypertrophy. Over the whole cardiac region there was a loud, rasping, systolic murmur, with the maximum of intensity over the base; there was also a slight murmur with the second sound." In our observations we endeavored, in the first place, to obtain tracings of the form of the pulse-wave. The dog was tied down firmly upon a dog-board and sphygmographic tracings were taken from the femoral artery by means of a Marey's sphygmograph. The most favorable tracings obtained, when the animal lay perfectly quiet and any irregularities resulting from psychic influences were excluded, were found, upon comparison with sphygmograms taken from the same artery in a healthy dog, to be entirely normal. The femoral arteries were then laid bare and a cannula introduced into each of them. One of the cannulas was connected in the usual way with a mercury manometer, which served to register arterial pressure; the other was connected with a Fick's "federkymographion" or spring-manometer. The object in using this latter instrument was to obtain some idea of the form of the pulse-wave in the opened artery. It possesses in a greater degree than any other instrument used for the same purpose, with the exception perhaps of Roy's sphygmo-tonometer, the two chief requisites of a true manometer, viz. a small mass and sufficient resistance to movement to overcome intrinsic vibrations. The pens of these manometers wrote upon the roll of paper of a Ludwig's kymograph in the same vertical line. A chronograph for marking seconds and a Marey's tambour for registering respiration were also made to write upon the same roll of paper. The animal was not at first under the influence of any anesthetic, the operation of laying bare the femorals being too slight to cause any serious pain. Afterwards, chloroform was given. It was noticed that when the animal was deeply under chloroform the heart-beats lost entirely an arhythmic character which had been very marked when the dog first came under observation, indicating that this irregularity had been caused before by psychic influences. The arterial pressure as given by the mercury manometer was good, ranging from 140 mm. to 150 mm. of mercury, which is within the limits of what can be called the normal blood-pressure of a dog. The pulse-wave given by the Fick manometer showed a sudden rise of pressure at the beginning of the wave corresponding to the sudden ejection of the contents of the left ventricle into the aorta at each systole, and then a much more gradual fall of pressure as the excess of blood in the arterial system was gradually forced through the capillaries into the veins. The descending limb of the wave was marked by a strong indentation. This indentation or dicrotism is, according to Fick, who has made a careful study of tracings obtained from dogs by means of his manometer, a characteristic of every true tracing, sphygmographic or manometric, of the pulse-wave. From a comparison of the tracings obtained from this dog with others obtained from healthy dogs, it would seem that the indentation was more strongly marked in this case. This is the only irregularity, if it is an irregularity, which could be seen in the tracings. The pulse rate varied from 156 to 180 per minute. The results of our observations, though mainly of a negative character, are not on that account less interesting. The fact that the animal kept up such an excellent arterial pressure is especially worthy of notice. The normal pressure in the pulmonary arteries, as observed by Beutner, Chaveau, and others, is not more than one-third as great as the pressure in the carotids of the same animal. Knowing this, and remembering at the same time that the lung-vessels possess great distensibility-can accommodate, in other words, a much larger quantity of blood than they usually contain, without any rise of pressure in the pulmonary arteries resulting, and further that they are probably subject to vaso-motor influences to a much smaller extent than are blood-vessels in other parts of the body, one would conclude, from à priori reasoning, that when this very extensive and distensible vascular region was thrown into free communication with the systemic circulation there would be a marked and permanent lowering of general blood-pressure. That this did not occur must be explained by a compensatory increase in the force of the heart-beat, or by an increase in the amount of peripheral resistance. The pressure in the pulmonary arteries must have been from two to three times greater than the normal pressure, requiring an increase in the force of the systole of the right ventricle to overcome this extra resistance, and causing a greater amount of blood to flow through the lungs in a given time into the left side of the heart. From the nature of the conditions governing the velocity of the blood current in the aorta and in the pulmonary artery it is not probable that there was any serious escape of venous blood into the systemic circulation. THE INFLUENCE OF VARIATION OF VENOUS AND OF ARTERIAL PRESSURE UPON THE CARDIOINHIBITORY ACTION OF THE PNEUMOGASTRIC NERVES. BY HENRY SEWELL, PH. D., Associate in Biology, Johns Hopkins University, and FRANK DONALDSON, JR., A. B. The studies which have been prosecuted in this laboratory upon the influences which modify the action of the isolated mammalian heart prove, if they prove anything, that the rate of discharge of muscular energy in the heart, considered by itself, is to a remarkable extent influenced by variations of blood pressure, either within or outside of that organ. All observers agree, however, that when blood pressure is altered within or outside of the non-isolated heart, the rate of beat is usually affected, and may be influenced in one of two ways-it either becomes quicker or slower. We know that the rate of the automatic discharge within the heart is under the control of two distinct nervous centres which lie within the brain; the excitement of one of these centres manifests itself in nervous impulses which quicken the heart-beat, while the irritation of the other centre has the effect of slowing the beat or causing it to cease altogether. These latter-the cardio-inhibitory impulses-arise from a definite locality in the medulla. Their course is along definite nerve fibres, which join near its origin the trunk of the pneumogastric nerve, and with the fibres of the latter are inextricably twined until they separate in the immediate neighborhood of the heart. When now the vagus nerve is cut in the neck of an animal and that part connected with the heart weakly stimulated with an electric current, the beat of the heart is slowed, and it is remarkable how definitely the extent of the slowing depends upon the strength of the stimulus used. When both vagi are divided the heart-beat becomes quickened and takes on a new rhythm; and finally, when the fibres of the sympathetic distributed to the abdomen are excited electrically, or by a blow on the abdomen, the heart may be stopped or slowed, both effects failing however if the vagi had been previously divided. In such an experiment we must presume that afferent impulses proceeded from the |