Some experimental observations on the innervation of the larynx in cats.

THE innervation and movements of the larynx have received the attention of many experimental investigators. It would be hard to find any series of results which has produced so many positively affirmed observations by many workers, with equally positive but exactly opposite results by many others. The experimental animals used have been varied and include rabbits, cats, dogs, goats, monkeys and finally man, and the only two generally accepted observations arising from the study of these species are that animal results cannot be applied with any certainty to man and that the larynx has as part of its raison d'etre a valvular function. That so little uniformity has been reached in the past 140 years since paralysis of the "cords" was observed by Legallois in sectioning both recurrent laryngeal nerves is sufficient to indicate the complexity of the problem. The copious literature on the subject bears further witness to that point and hence it is not without some trepidation that the following brief communication, relating to the experimental investigation of the larynx and its innervation, is contributed. The animals used were adult cats on the whole and the sole reason for this selection was that other experimental procedures were being undertaken concurrently which, quite unrelated to this particular subject, afforded an opportunity to make the observations reported below. All that has been attempted was to observe the following effects: 1. Gradually increasing stimulation on the recurrent laryngeal nerve in the assumption that the various fibre sizes have different chronaxies. 2. Altering the physiological state of the nerve and again applying gradually increasing stimuli. 3. Stimulation experiments on the superior laryngeal nerve and its branches. All these effects were watched by direct laryngoscopy and the movements evoked were recorded by cine photography.