2 3 8 A MANUAL OF PHYSIOLOGY 



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 permanent 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 tfyen become gradually 

 shallower again, till they cease for the next pause. The pheno- 

 menon 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 resuscitation of the respiratory centre. 

 In frogs, Cheyne-Stokes breathing has been observed as the result 

 of interference with the circulation in the spinal bulb, ' drown- 

 ing,' 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 apnoea, the respira- 

 tion, 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. 232) 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 stimulates 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 breathing be- 

 comes quite deep or actually dyspnoeic. The store of oxygen is 

 replenished by this thorough ventilation of the lungs, the changes 



