The contractions which are excited in the heart by application of local stimuli would seem to indicate more clearly that the ganglia are reflex centres. When a heart has just ceased pulsating application of a stimulus gives rise to a contraction affecting the entire organ, the contraction, too, taking place in the same rhy thmical manner in which it takes place during life. After some time, the stimulus, when again applied, gives rise to a contraction which does not affect the entire organ, but only the particular auricle or ven tricle to which it is applied, and after some time farther the same stimulus gives rise merely to local contractions. The former two seem to be, as Volkmann regards them, movements of reflex action, while the last is a mere stimulus movement. The circumstance that stitnulus applied to the ventricles in such a heart gives rise to contractions which com mence in the auricles, and therefore at a point distant from that to which the irritation has been applied, seems explicable only on the supposition that the impression thereby pro duced is conveyed to a nervous centre, and here transferred to fibres proceeding to the part in which the contraction commences.
The following experiment of Volkmann would also appear to favour the view in ques tion. He destroyed the spinal cord in a newly beheaded frog, and satisfied himself that no reflex action could be produced in the voluntary muscles. The heart was then laid bare, and during an interval of 101 minutes its pulsations were counted at fourteen dif ferent times. Five minutes after destruction of the central organs they numbered 72 per minute ; thirty minutes afterwards they were 48 per rninute. After this they were found to average between 45 and 51 per minute. He then crushed with the blow of a hammer one of the hind feet ; and now, during the 104th minute after the spinal cord had been de stroyed, counted 70 pulsations. Thus, then, two hours after the operation of destroying the spinal cord, we have a sudden increase of 20 beats in the minute, which admits of hardly any other explanation than that given by Volkmann, that it was due to the stimulus ap plied to the foot being reflected to the nerves of the heart through the ganglia of the sym pathetic.
Influence of the sympathetic on the vegetative processes. — According to some, these pro cesses go on independently of any influence exercised by the nervous system, while others maintain that the two are more or less in timately connected. Of the latter some believe that the sympathetic is the only part of the nervous system by which such influence is exercised, while others hold that it exercises no influence in this respect which is not also exercised by the cerebro-spinal system.
There can be no doubt that in the plant the processes of nutrition take place without the co-operation of any nervous influence; and in the same way in the embryo of all animals they go on for some time before any trace of nervous tissue has appeared. In the animal after birth, however, they appear to be more or less influenced by the nervous system. This is rendered probable by several circumstances, such as the effects of various powerful mental etnotions and of morbid states of the nervous system upon digestion, on the secretion of the saliva, tears, &c. ; the effects of the same upon the heart and capillary vessels. This is also shown by the changes which take place in the nutrition of parts, when the nerves by which they are supplied have been divided, or after lesions of the brain or spinal cord. Thus, as shown by
Magendie, section of the fifth nerve is very quickly followed by distension of the blood vessels and inflammation of the conjunctiva, sclerotic, and other parts of the eye, which may terminate, in the course of two or three weeks. in complete disorganisation of the eyeball. It has also been found that sec tion of the nerves of a broken limb prevents the due formation of callus. The experi ments of Drs. Sharpey and Daly on the salamander also prove that parts are repro duced much more slowly and less perfectly when the spinal cord has been destroyed to a certain extent than under opposite circum stances. When wounds are inflicted upon both limbs of an animal, and the nerves of the one limb are divided while those of the other limb are left entire, it has been found that while a lively inflammation and normal suppuration take place in the wound of the limb the nerves of which have been left en tire, the wound in the limb whose nerves have been cut scarcely inflames at all, and only a thin unhealthy discharge is formed. Lesions of the spinal cord have also been observed to be followed sonietimes by morti fications of the paralysed limbs, and this with such rapidity as would seem to indicate that they stand to one another in the relation of cause and effect. The tendency to sloughing observed in typhus and other diseases at tended with great depression of the functions of the nervous system would also seem to indicate connection between the nutritive pro cesses and the nervous system.
It has been already noticed that branches of the sympathetic pass along with the arte ries in considerable numbers; some of them being apparently distributed to their coats, while others accompany them into the sub stance of the different glandular organs. It has also been stated that sympathetic fibres have been observed to join the cerebro-spinal nerves, and to run peripherically with them to the different organs of animal life. From this distribution of the sympathetic, it has been held that it is in a peculiar manner connected with the nutritive processes. That it does exert an influence over the nutritive pro cesses is seen from the effects which follow division of its branches. In addition to con traction of the pupil section of the sympa thetic in the neck has also been observed to be followed by a disturbed state of the cir culation in the eyeball, giving rise to swelling and inflammation of the cornea, a shrinking of the eyeball, and at the same time to an increase in the lachrymal secretion. In some of the experiments of Dr. John Reid, the in jected state of the conjunctiva took place in the course of a few minutes after the opera tion. In a dog, in which he had divided the common trunk of the vagus and sympathetic as high up as possible, Valentin * observed that the secretions of the eye were very much increased, remaining so even after the lapse of several months. The same effects were also observed by hint after extirpation of the superior cervical ganglion in the same animal. Dupuy found, on removing the superior cer vical ganglion of both sides in the horse, that besides the effects above described the opera tion was followed by an anasarcous condition of the limbs and an eruption on the whole cutaneous surface.