Permanent Devocalization of Dogs by Removal of both the True and the False Vocal Cords

In many institutions where it has been necessary to devocalize the laboratory dogs the results have not been satisfactory. In 1932 the writer made a study of the usual devocalizing methods with the object in view of improving the results obtained from such methods.

By using a pair of Miles nasal cutting forceps it was found that the true vocal cords could be rapidly and completely removed. 1 The procedure was carried out on 20 dogs under morphine-ether anesthesia. There were no complications and the animals recovered within 24 hours. After about 3 months, however, each dog developed a hoarse, unpleasant bark. The immediate assumption was that the operative technic had been faulty and that the vocal cords had not been completely removed. Later, when some of the same animals came to autopsy, laryngeal examinations showed a complete absence of the true vocal cords. Further studies of the autopsy material revealed in each case a well developed pair of soft mucous folds or pockets at the base of the epiglottis and just above the true vocal cords. These folds were identified as false vocal cords and seemed to be the only remaining structures by the use of which sound might be made.

The surviving dogs whose vocal cords had been removed with poor results were again prepared for operation. The soft folds or pockets of the false cords were removed as completely as possible with a pair of straight, back-cutting Ostrom forceps. Upon recovery these animals were no longer able to produce any noise other than soft whispered sounds even with their most vigorous barking efforts. Since that time approximately 200 animals have been devocalized by the method of removing both the true and false vocal cords.