REGULATION OF RESPIRATORY MOVEMENTS 1215 



In studying the nervous mechanism of respiration, it is necessary to have 

 some accurate method of recording the respiratory movements. They may be 

 registered by means of a tambour applied to the chest, communicating with 

 another tambour provided with a lever, which is arranged to write on a blackened 

 surface ; or a side tube to a cannula in the trachea may be connected with 

 the registering tambour. In the first case movements of the thorax are registered ; 

 in the second changes of intra -pulmonary pressure. These methods are obviously 

 useless when it is wished to study the effects of artificial distension or collapse 

 of the lungs. In this instance we may use the ingenious method described by 

 Head. In the rabbit a slip of the diaphragm on either side of the ensiform 

 cartilage is so disposed that the end of it may be freed and attached by a thread 

 to a lever without injury to its blood- or nerve-supply. It is found that this 



FIG. 507. Normal tracing of diaphragm slip (Head's method). 



slip contracts synchronously with the rest of the diaphragm, so that it serves as 

 a sample of the diaphragm, the contractions of which may be recorded uninfluenced 

 by passive movements of the chest wall or artificial increase of mtra-pulmonary 

 pressure. 



If, while the respiratory movements are being recorded in one of 

 the afore-mentioned ways, both vagi be divided,* a marked change 

 in the respiratory rhythm is at once seen. The first effect is an increased 

 inspiratory tonus, but this rapidly disappears, and the respiratory 

 movements become less frequent and are increased in amplitude. If 

 now the central end of one of the vagi be stimulated with an interrupted 

 current, the respiration may be quickened, or, as is more commonly the 

 case, the inspiratory movements may be increased at the expense 

 of the expiratory, so that finally a condition of inspiratory standstill 

 is produced, and the slip of the diaphragm enters into prolonged 

 contraction. 



With a very weak stimulus it is sometimes possible to produce 

 augmentation of the expiratory movements or rather inhibition of the 

 inspiratory, and this is the invariable result of passage of a constant 

 current through the vagus in an ascending direction. This effect may 



* The division of the vagi is best effected by putting them on a hooked 

 copper wire, of which the upper end is inserted in a f reezing-mixture. In this way 

 complete functional division of the nerves is obtained without any excitation. 

 If the nerves be cut, a certain amount of stimulation takes place in comtequence 

 of the closure of the demarcation current produced by the cross-section. 



