xiii RESPIRATORY RHYTHM 453 



necessity for breathing is relieved by devices very far from ordinary. 

 The inspirations are taken at rare intervals, and are deep and 

 quickly completed ; they occur at irregular intervals, and at 

 moments when the phonetic pauses are effective in expression ; the 

 expirations, on the contrary, are prolonged and often very power- 

 ful, since the expired air is employed wholly in the service of 

 phonetic expression. So, too, in sucking, swallowing, vomiting, 

 defaecation, and parturition, the mechanics of respiration (as we 

 shall see elsewhere) assume different forms and attitudes. Laughing, 

 crying, sobbing, yawning, represent so many typical expressions of 

 feeling, which all, as we have seen, consist essentially in special 

 forms of the respiratory movements. Fear, joy, expectation, pre- 

 occupation, are states of mind continually associated with 

 respiratory changes, which are conspicuous enough, even if less 

 characteristic than the preceding. The direct control of the will 

 is only exerted upon the respiratory movements under quite special 

 conditions e.g. we hold our breath when we know the air to be 

 foul or stagnant, when we dive into water, or under other similar 

 conditions. 



All these psychical modifications of the respiratory rhythm are 

 governed by impulses emanating from the cerebral cortex, 

 particularly from that region known as the motor area. When 

 this tract is stimulated electrically in the dog or cat, the respiratory 

 movements are visibly accelerated or retarded, which depends less 

 on the seat than on the intensity of stimulation. According to 

 Frangois-Franck, strong stimuli retard the respiratory processes ; 

 weak stimuli accelerate them. 



The sub-cortical centres are also capable of modifying respiratory 

 rhythm. On exciting the surface of a section, at the level of the 

 anterior and posterior corpora quadrigemina, Martin and Bocker 

 obtained unmistakable inspiratory effects. Christian! found the 

 same on exciting the floor of the third ventricle. When, on the 

 other hand, he excited the grey matter, at the entrance of the 

 Sylvian Aqueduct, he obtained expiratory effects. 



These different parts of the brain (and probably others not yet 

 investigated because less accessible) affect the respiratory move- 

 ments, in so far as they are capable of modifying the rhythmical 

 activity of the bulbar respiratory centre, with which they are 

 connected by means of special descending nerve tracts. Evidence 

 for this is afforded in the fact that the clean division of brain 

 from bulb at the level of the upper limit of the pons, has, as we 

 have seen, only a transient effect on respiratory rhythm. This 

 shows that even under normal conditions the cerebral respiratory 

 centres take no active part in modifying the impulses sent out 

 from the bulbar centre. We shall, however, see under what 

 abnormal circumstances the influence of the cerebral respiratory 

 centres is functionally apparent in its full importance. 



