RELATION OF RESPIRATION TO THE NERVOUS SYSTEM 287 



one lung, followed after an interval by section of the opposite vagus 

 in the neck, is not fatal in rabbits. This is also in favour of the view 

 that in double vagotomy the stress falls mainly on the digestive system . 



Innervation of the Bronchial Muscles. Both constrictor and 

 dilator fibres for the bronchi are contained in the vagus. They are 

 not constantly in action, but can be reflexly excited, most easily 

 (in the dog and cat) by stimulating the nasal mucous membrane, 

 and particularly a small area well back upon the nasal septum. 

 Cauterization of the corresponding area in man is said to give per- 

 manent relief in certain cases of spasmodic asthma, a condition in 

 which the recurrent attacks of dyspnoea seem, according to the most 

 generally accepted view, to be associated with spasm of the bronchial 

 muscles. 



Special Modifications of the Respiratory Movements. Cheyne- 

 Stokes Respiration is the name given to a peculiar type of breathing, 

 marked by pauses of many seconds alternating with groups of 

 respirations. In each group the movements gradually increase to 

 a maximum amplitude, and then become gradually shallower again, 

 till they cease for the next pause. The phenomenon often occurs in 

 certain diseases of the brain and of the circulation, and pressure on 

 the spinal bulb may produce it. In cats in which the circulation 

 in the brain and medulla oblongata has been interrupted for a time 

 and then restored it is often noticed at a certain stage of resuscita- 

 tion of the respiratory centre. In frogs, Cheyne-Stokes breathing 

 has been observed as the result of interference with the circulation 

 in the spinal bulb, ' drowning,' or ligature of the aorta, and also as 

 a consequence of removal of the brain, or parts of it (hemispheres 

 and optic thalami). But it is not peculiar to pathological conditions, 

 being also seen, more or less perfectly, in normal sleep, especially in 

 children, in healthy men at high altitudes, in hibernating animals, 

 and in morphine and chloral poisoning. 



Well-marked Cheyne-Stokes breathing can be obtained experi- 

 mentally in normal persons in a variety of ways. If, for example, 

 the subject is caused to breathe deeply and frequently for about two 

 minutes, so as to produce a prolonged apncea, the respiration, when 

 it is resumed spontaneously, is of the Cheyne-Stokes type (Haldane). 

 The explanation given by Haldane is that the fall in the partial 

 pressure of the oxygen in the pulmonary alveoli (p. 283) during the 

 primary apnoea, with the consequent fall of oxygen pressure in the 

 arterial blood and the respiratory centre, leads to the production 

 of lactic acid in the respiratory centre and elsewhere, which stimu- 

 lates the centre in the same way as carbon dioxide, and thus, permits 

 it to be excited by a smaller partial pressure of carbon dioxide than 

 that normally necessary. As soon as the pressure of carbon dioxide, 

 which is increasing during the period of apnoea, has reached the 

 exciting value breathing is resumed. The respirations, beginning 

 as very feeble movements, rapidly increase in strength till the 



