vii THE MEDULLA OBLONGATA 399 



cardia and dyspnoea may become so marked that the animal dies 

 in a few hours, owing merely to the cessation in the control of 

 respiration and circulation. In fact no lesion of the internal 

 organs sufficient to account for death can be detected by post- 

 mortem examination. 



In other cases the animals survive the double vagotomy for a 

 longer period, and death is due to hepatisation of the lungs, particu- 

 larly of the upper lobes, or to haemorrhage or hyperaemia with 

 diffuse oedema of the lungs and excess of mucus. 



Like the panophthalmia after section of the trigeminal nerve 

 (see pp. 330 et seq.), the pneumonia that follows vagotomy was long 

 regarded as a proof that the vagi contained fibres with a trophic 

 influence on the pulmonary tissue. Traube was the first who 

 threw doubt on this theory. He noted after double vagotomy 

 difficulty in swallowing, owing to the paralysis of the glottis and 

 oesophagus ; bits of food, saliva, or buccal mucus may consequently 

 get into the air passages or stick in the oesophagus and give rise 

 to frequent regurgitation, in which particles may penetrate through 

 the open glottis into the lungs, and there set up inflammation. 



Again, apart from the penetration of irritating substances by 

 the air passages, the pulmonary lesions consequent on double 

 vagotomy may be explained by the following facts : 



(a) Vagotomy causes motor and sensory paralysis of the larynx, 

 trachea, the bronchi, and pulmonary alveoli, which, besides produc- 

 ing pulmonary emphysema and catarrh of the bronchi, suppresses 

 coughing and favours irritation, not only by foreign bodies, but 

 also by the mucus secreted by the bronchi. 



(&) The acute dyspnoea consequent on double vagotomy 

 hinders the pulmonary circulation, and eventually produces 

 marked pulmonary congestion with haemorrhage and oedema, 

 even independently of the vasomotor paralysis of the lung which 

 was insisted on by Schiff and Herzen, but for which there is no 

 direct evidence. 



When an interval of several months intervenes between the 

 section of the first and second vagus, so that the nerve first divided 

 is able to regenerate, dogs not infrequently survive double vagotomy 

 (Vanlair), but not rabbits or guinea pigs (Beaunis). It is, how- 

 ever, difficult to decide what length of time must elapse between 

 the first and second vagotomy, in order to ensure regeneration and 

 therefore survival. Vanlair's dogs died one to eight days after the 

 second vagotomy when the first had been made four, six, seven 

 months or even a year previously. But as one dog survived 

 when the second vagus was cut ten months after the first, he 

 concluded that at least ten to twelve months were essential for 

 complete regeneration of the vagus first divided. 



Later work has proved, however, that independently of the 

 regeneration of the nerve first divided, dogs may survive for 



