464 PHYSIOLOGY CHAP. 



ments succeed each other with marked retardation; the inspirations 

 become deeper and are followed by long pauses (inspiratory 

 tetanus) ; the expirations are rapid, with active intervention of 

 the abdominal muscles, and are followed by brief pauses ; at the 

 same time the normal rhythm, i.e. the regular succession of 

 inspirations and expirations, remains unaltered. These effects 

 may vary in intensity, and inspiratory tetanus is sometimes 

 absent, in accordance probably with the varying degree of 

 operative traumatism and consequent haemorrhage. But in all 

 cases the amplitude of respiration or pulmonary ventilation in the 

 unit of time is diminished by about one-half, so that the animal 

 no long time after succumbs to asphyxia. 



These striking results, as disclosed by the researches of 

 Marckwald in Kronecker's laboratory (1887), and confirmed in 

 essentials by Loewy in Zuntz' laboratory (1888), show the great 

 importance assumed by the functions of the centres and afferent 

 nerve-paths from brain to spinal bulb in pulmonary respiration, 

 when the vagi, which normally regulate respiratory rhythm, are 

 cut off. While, however, the afferent vagus tracts to- the bulbar 

 respiratory centres are able perfectly to compensate the deficit in 

 the cerebral paths, these last are only partially able to compensate 

 for the failure of the vagus. The effects of double deficiency show 

 'that the whole of the other afferent paths to the respiratory centres 

 which remain intact, after section of the vagi and separation of 

 the brain from the bulb, are incapable of influencing the said 

 centres so as to provide the respiratory movements essential for 

 adequate pulmonary ventilation. 



Among these afferent nerve-paths, special mention must be 

 made of the trigeminus, to which the nasal mucosa owes its 

 sensibility ; the superior and inferior laryngeal branches of the 

 vagus, which contain the sensory fibres to the laryngeal and 

 tracheal mucosa ; and the glosso-pharyngeal, which serves the 

 specific sensibility of the tongue and pharynx. All these paths 

 are in special relation with the expiratory centres, and their 

 stimulation, whether at the peripheral ending or along their 

 course, almost invariably produces expiratory effects. 



We know how readily sneezing is induced by chemical excita- 

 tion of the nasal mucosa. Its electrical stimulation produces 

 expiratory arrest (Hering and Kratschmer). Expiratory standstill, 

 or a true expiratory tetanus, can also be elicited by stimulation of 

 the endings of the trigeminus, which are distributed to the skin of 

 the face, if a large surface is excited, e.g. if the animal's head is 

 dipped into water. 



Coughing is produced by the stimulus of foreign bodies upon 

 the mucosa of the larynx and windpipe, transmitted more 

 particularly by the afferent paths of the superior and inferior 

 laryngeals. Gentle electrical stimulation of the superior laryngeal 



