REGULATION OF THE RESPIRATORY MOVEMENTS 1139 



It is an interesting question whether the electrical excitation of nerves 

 may not be due to a similar alteration in the hydrion concentration at the 

 cathode which is the seat of stimulation. If this were so, all the activities 

 of protoplasm might be regarded as determined by the relative concentration 

 of the H and OH ions within the cells or in the medium surrounding the cells. 



THE REFLEX NERVOUS REGULATION OF RESPIRATION 



Although the specific sensibility of the respiratory centre to C0 2 is the 

 most important factor in determining the depth and rhythm of the respiratory 

 movements, these movements and the condition of the respiratory centre 

 itself are modified in a large degree by impulses arriving at the centre along 

 both vagi. Through other sensory nerves of the body the respiratory 

 movements can be altered reflexly, but it is only through the vagi that a con- 

 tinuous stream of impulses passes to the centre under normal circumstances, 

 so that every respiratory movement is modified by these impulses. 



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 e'ffects 

 of artificial distension or collapse of the lungs. In this instance we may use the 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 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 move- 

 ments of the chest wall or artificial increase of intra-pulmonary pressure. 



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

 afore-mentioned ways, both vagi* be divided, 1 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 move- 

 ments 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 in- 

 spiratory 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. 



1 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 freezing-mixture. In this way complete func- 

 tional division of the nerves is obtained without any excitation. If the nerves be cut, 

 a certain amount of stimulation takes place in consequence of the closure of the demarca- 

 tion current produced by the cross-section. 



