FUNCTIONS OF THE MEDULLA OBLONG ATA. 517 



divided, the respiration becomes slower ( J. Reid), as if the 

 necessity were less acutely felt : but it does not cease, and 

 therefore other nerves besides them must have the power 

 of conducting the like impression. The experiments of 

 Yolkmann make it probable that all centripetal nerves 

 possess it in some degree, and that the existence of imper- 

 fectly aerated blood in contact with any of them acts as a 

 stimulus, which, being conveyed to the medulla oblongata, 

 is reflected to the nerves of the respiratory muscles : so 

 that respiratory movements do not wholly cease so long as 

 any centripetal nerves, and any nerve supplying muscles 

 of respiration, are both in continuous connection with the 

 respiratory centre of the medulla oblongata. The circula- 

 tion of imperfectly aerated blood in the medulla oblongata 

 itself may also act as a stimulus, and react through this 

 nerve-centre on the nerves which supply the inspiratory 

 muscles. 



The wide extent of connection which belongs to the 

 medulla oblongata as the centre of the respiratory move- 

 ments, is further shown by the fact, that impressions by 

 mechanical and other ordinary stimuli, made on many 

 parts of the external or internal surface of the body, may 

 induce respiratory movements. Thus involuntary respira- 

 tions are induced by the sudden contact of cold with any 

 part of the skin, as in dashing cold water into the face. 

 Irritation of the mucous membrane of the nose produces 

 sneezing. Irritation in the pharynx, oesophagus, stomach, 

 or intestines, excites the concurrence of the respiratory 

 movements to produce vomiting. Violent irritation in the 

 rectum, bladder, or uterus, gives rise to a concurrent action 

 of the respiratory muscles, so as to effect the expulsion of 

 the faeces, urine, or foetus. 



The medulla oblongata appears to be the centre whence 

 are derived the motor impulses enabling the muscles of 

 the palate, pharynx, and oesophagus, to produce the suc- 

 cessive co-ordinate and adapted movements necessary to 



