176 THE BODY AT WORK 



tion of dyspnoea, which ends in death. When the central end 

 of the cut vagus is stimulated, the movements become more 

 natural. Clearly, the respiratory reflex is not dependent 

 upon the vagus, since it continues after the nerve is cut, 

 although the impulses which pass up this nerve regulate its 

 rhythm. They govern the length of the inspiratory move- 

 ments, cut them short at the right moment, and secure their 

 succession at proper intervals. 



The transfer of afferent impulses into efferent channels 

 occurs in the medulla oblongata. Long ago it was found that 

 if the brain above this level be removed, part by part, respira- 

 tion is not interfered with until the medulla oblongata is 

 injured. When a cut is made into the floor of the fourth 

 ventricle not far to one side of the middle line, the respiratory 

 movements on that side of the body cease. If the injury be 

 bilateral, even though very limited in extent, respiration stops. 

 This spot was therefore spoken of as the " respiratory centre." 

 Flourens, who first discovered it, believed that it was a 

 mere spot. He gave to it the fanciful name of nceud vital. 

 It is the place at which the afferent nerves which call for 

 respiration are brought into connection with all the various 

 motor nerves which bring about the respiratory movements 

 of nostrils, larynx, chest, and diaphragm. Possibly the knife 

 in Flourens' incision divides the tract of fibres which distri- 

 butes afferent impulses, but whether the junction be a defined 

 tract or no, injury to this region of the medulla throws the 

 nervous mechanism of respiration out of gear. At this par- 

 ticular spot lies the " centre " for respiration the one part 

 of the nervous system which must be intact if the movements 

 of respiration are to be carried out. There is no reason for 

 thinking that respiratory impulses are generated at this spot. 

 It is a centre in the same sense in which Crewe is a centre for 

 distributing the goods of Lancashire and other parts of England 

 to North Wales. The use of the term " nerve-centre " has been 

 very much abused. Centres were supposed to be collections 

 of cells, each group of which had some prerogative of initiation. 

 Reasoning from the analogy of human institutions, it was 

 thought necessary that the nervous system should be organized 

 into departments severally responsible for the administration 

 of the activities of certain sets of muscles : one centre controlled 



