Rabbits, non-anaesthetized or urethanized, cats, urethanized, and dogs under ether or morphine were experimented on.
Since various kinds of animals, of anaesthesia and of stimulation were used and various phenomena yielded as the outcome, it is rather difficult to present them briefly but thoroughly. Only an outline of the results is given in this paragraph. The description begun at p. 191 can be rather taken as a detailed summary of this paper.
At first it may be pointed out by comparing the previous reports with the present investigations that it is dangerous to apply the results obtained in one kind of vertebrate, by one kind of anaesthesia and one kind of stimulation to all others.
While the vagus tone is in dogs absent under ether, but a high tone is developed unter morphine, a well known fact, the accelerators have a somewhat significant tonicity regardless of the kinds of narcosis, so that the interference with the cardio-acceleratory nerves resulted in a reduction of 70-80 beats a minute.
Sensory stimulations, such as the injection of 70% alcohol solution into the nose or mouth, mechanical compression of the eye-ball, stimulation of the crural nerve and asphyxia occasioned in rabbits mainly retardation, in cats mainly acceleration, and cases of retardation were somewhat more frequently met with in dogs. Asphyxia only caused cardiac slowing in cats also.
Double vagotomy resulted in rabbits in an increase of cases of cardiac reflex acceleration and diminution of those of retardation, that is to say, the cardiac reflex of a not so insignificant mass persists the bilateral section of the vagus nerve. The reflex alteration in the heart rate was observed also in the doubly vagotomized cats and dogs, the frequency of cases in which the alteration of the rate did not take place being nearly the same as with the animals with intact heart innervation.
A comparison of the data on the doubly vagotomized and splanchnicotomized cats and dogs with those of the animals deprived of the vagi, accelerantes and splanchnici may justify us in recognizing the rôle played by the cardio-accelerator nerves in the reflex acceleration of the cardiac rate. In view of the fact of the increase of the epinephrine liberation in cases of stress, such as sensory stimulation, asphyxia, etc., it may not be justifiable to draw any definite conclusion as to the significance of the cardio-accelerator nerves by comparing the reflex alterations in the heart rate caused by an agent before double vagotomy, after it, and after further addition of section of the cardio-accelerator nerves, unless the other factor, which intervenes in affecting the denervated heart rate reflexly, that is the secretion of epinephrine is ruled out.
The section of the vagi, accelerantes and splanchnici left a trace of the reflex alteration in the cardiac rate, though not so frequently.
That the vagus nerve induces the reflex-inhibition by an increase of its tone and the reflex-acceleration by decrease of the same was repeatedly proved in the present investigations. The similar functioning of the accelerantes (the inferior cervical and stellate ganglia) was also detectable, though it was small and infrequent. In the cats under our experimental conditions it was proved only with some difficulty that the vagus and accelerantes play some rôle, though not a significant one, in the cardiac reflexes.
The effects of the various stimuli employed in this investigation upon the cardiac rate were by no means identical with each other. Only briefly stated, -in the rabbits the cardiac slowing was a rather frequent occurence in general, but there was evidently a great difference in the inhibiting power among the stimuli. Asphyxia was the most potent agent in causing cardiac slowing and the pressing on eye was the weakest. In cats reflex-acceleration was rather frequently a result, the stimulation of the oral mucosa being found as most powerful.
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