SOME OBSERVATIONS ON THE BUCCO‐PHARYNGEAL STAGE OF REFLEX DEGLUTITION IN THE CAT

Abstract

1. A method is described for obtaining speedily, under deep narcosis, by ablation of the whole cerebrum and the greater part of mesencephalon, a mammalian reflex preparation yielding uniform reactions. In this preparation the floor of the oral chamber and the faucial and narial entrances into pharynx lie freely exposed; opportunity is thus given for direct inspection of the first phases of deglutition. Observations on reflex deglutition in this preparation are described.2. Localised moderate pressure applied to points in an area about 2·5 cm. long on the back wall and slope of the roof of the pharynx evoked the swallow readily. Similar pressure applied to the soft palate, epiglottis, and hyo‐epiglottidean part of the dorsum of the tongue evoked the swallow less readily than did such pressure in the above area.3. Water and watery fluids introduced even in very small quantity—e.g. 1 c.c.—over the extreme posterior part of the tongue evoked deglutition in the preparation with readiness and regularity. A larger dose evoked the swallow more quickly than a smaller one.4. Some fluids were found to excite swallowing more readily and potently than others. Dilute alcohol was the most markedly phagetic agent we met with, considerably more potent even than water or saliva. Glycerine evoked reflex swallowing markedly. On the other hand, the oils tried—olive oil, cod liver oil, and castor oil—excited swallowing very poorly; they were practically aphagetic. Addition of alcohol to an aphagetic oil gave a mixture of good phagetic power; thus, although a dose of castor oil scarcely excited swallowing at all, a dose of similar volume made up of three parts of the oil with one part of ethyl alcohol excited swallowing readily and powerfully.5. Noxious fluids and fluids distasteful to the normal cat evoked the swallow readily in the purely reflex animal; after some repetitions, however, they induced reflex rejection, retching, etc., in place of swallowing.6. Solid boluses—e.g. pieces of meat—were, in our experience with this preparation, much less effective as stimuli than were even a few drops of the phagetic fluids—e.g. water.7. In our preparation on administration of a dose of fluid to the preepiglottidean region of the tongue the first movement excited was very commonly a brief depression and cupping of the back part of the tongue, and this immediately preceded the powerful lifting and bunching up of the tongue, the essential tongue movement of the bucco‐pharyngeal swallow. Excision of the whole soft palate did not render ineffective, or obviously impair, the swallowing of a dose of fluid, even when the preparation was inverted—i.e. supine.8. Faradisation of the lingualis branch of trigeminus and of the afferent fibres of nervus intermedius (chorda tympani) inhibited the buccopharyngeal swallow, either prolonging the latency of the latter or suppressing it temporarily altogether. But the inhibition was not powerful or long‐lasting.9. From the fovea inferior of the floor of the IVth ventricle weak faradisation with the stigmatic electrode by the unipolar method excited swallowing readily and regularly. With weak currents no other point in the floor of the ventricle produced this effect. Simultaneously with the swallowing the foveal stimulation caused arrest of the respiratory movements of larynx and chest, as in normal swallowing; also a change in pulserate, as in normal swallowing.10. Under employment of stimulation of the fovea observations were made on facilitation, summation, refractory phase, and the all‐or‐nothing feature of the reflex swallow.11. In the reflex preparation the arrest of breathing which accompanies swallowing was studied by the graphic method. The disturbance to respiratory rhythm caused by swallowing a small dose, e.g. 25 c.c., of dilute (25 per cent.) alcohol was found to be much greater than that caused by swallowing a much larger dose, e.g. 2 c.c., of water.12. The slowing of pulse and accompanying fall of arterial pressure occurring during swallowing were set aside by atropine.The expenses incurred in making the experiments were in part defrayed by a grant kindly allowed by the Committee of the Royal Society administering the Government Grant Fund.