It has also been observed that in the heart of the frog there is one portion of the septum between the auricles which continues its con tractions much longer than any other part ; and in this portion the greatest number of the cardiac ganglia and nerves are situated. It was also observed by Kffiliker that the trans verse groove in the frog's heart in like manner exercised a marked influence on its rhythmical contractions ; and here also the ganglionic corpuscles and nerves are very abundant. In young kittens and rabbits also, Valentin has likewise observed that the groove in question affects the movements of the heart very much.
The opinion of' Volkmann, therefore, that the rhythmic contractions or the heart are connected with a nervous centre, and more over that this nervous centre is the sympa thetic ganglia contained in the heart's sub stance, seems highly probable. At the same time there cannot be the least doubt that an influence may be exercised over these move ments by the central masses of the nervous system.
Intestinal canal. CE sophagus.— The ceso phagus receives nerve-fibres both from the pneumogastric and sympathetic. The former is, according to Longet #, the source of its sensibility as well as of its motion, while the sympathetic presides over the secretion of the mucus with which its inner surface is lubri cated. Valentin, however, as mentioned by Longet, found, on irritating the cervical por tion of the main cord of the sympathetic in the rabbit, that movements were pro duced in the middle portion of the ceso phagus ; and contractions were also produced in the thoracic portion of the same tube when the inferior cervical ganglion or either of the first four thoracic ganglia was irritated.
Lon get, on repeating the experiments of Valen tin, failed to observe any contractions, and concludes that Valentin must have irritated the pneumogastric as well as the sympathetic. It is only (according to Longet) when the pneumogastric or spinal nerves are irritated, that such contractions ensue ; and, moreover, section of the eighth pair is attended by com plete paralysis of the cesophagus.
Stomach.—The stomach, like the cesopha gus, is supplied by branches of the pnetimo gastric and sympathetic. Irritation of the former is almost always followed by con tractions in this organ. Irritation of the splanchnic nerves, or of the semilunar gan glion, according to Longet*, produces no such effect. Valentin, on the other hand,
found that stimulus applied to the main cord of the sympathetic in the neck, or to the in ferior thoracic ganglia, in the rabbit, gives rise to contractions in this organ. Volkmannt has also found that when the stimulus of the electro-magnetic rotation apparatus is applied to the thoracic portion of the sympathetic in the cat it gives rise to powerful peristaltic movements in the stomach. Ile also observed still more lively contractions excited in the stomach of a young dog when the same sti mulus as in the previous experiment was applied to the sympathetic cord in the thorax, or to the greatcr or smaller splanchnic nerves before they enter the semilunar ganglion. It would seem, therefore, that, besides the motor filaments which are sent to the stomach by the pneumogastric, it also receives others through the medium of the sympathetic.
As regards the movements of the small intestine, Szc., it is almost invariably excited to contraction by irritation of the splanchnic nerves or semilunar g,anglion. After the movements produced in the intestine by the stimulus of the air, acting upon them when the cavity of the abdomen is laid open, have subsided, contractions extending over the greater part of the gut may still be produced, as NS as first shown by- 'liner, by application of chemical irritants, such as potash, to the solar plexus. According to Valentin, the niove ments produced by irritation of the splanchnic nerves are chiefly confined to the duodenum and upper part of the jejunum, while irritation of the solar plexus, on the other hand, is fol lowed by contractions which extend over the whole of the small intestine. Irritation of the sympathetic cord in the thorax as high up as the fifth or sixth ganglion, and also in the lum bar region, gives rise, according to Valentin, to distinct contractions in the small intestine, while stimulus applied to the lumbar and sacral portions acts very energetically upon the great intestine and rectum. The influence of the sympathetic over the movements of the intestines is also shown by the observation of Valentin that when the branches which pass along the mesentery are irritated, con tractions are produced in the particular por tions of the intestine to which they are dis tributed, while the rest of the gut remains quite motionless.