472 PHYSIOLOGY CHAP. 



that the respiratory rhythm is modified, becoming more frequent 

 and perfectly synchronous with the rhythm of the artificial stimuli. 

 Again, the polypnoea induced in man by rhythmical exercises which 

 impart considerable vertical oscillations to the torso (running, 

 jumping), is characterised by a tendency to synchronisation 

 between the respiratory phases and the rhythm of rise or fall of 

 the centre of gravity. These rhythmical movements of running 

 or jumping must, therefore, determine afferent nerve impulses to 

 whose rhythm the respiratory centre tends to adjust the rhythm 

 of its own proper activity. And since the rhythm of the afferent 

 nerve impulses is in these cases more frequent than the rhythm of 

 normal respiration, dyspnoea ensues as the direct effect. 



This theory also explains certain peculiarities of the said 

 dyspnoea ; for example, the fact of its rapid onset, at the very 

 beginning of the running and jumping, i.e. before it is possible to 

 assume any production of toxic substances or rise of tempera- 

 ture, such as are invoked in the preceding theories. So, too, 

 its immediate disappearance, sometimes at the very moment 

 the exercise is over. On this theory, again, it is easy to explain 

 the other fact known to professional athletes, to wit, that properly 

 trained runners are able to hold out for a long time without 

 experiencing dyspnoea. 



" We can also understand " (adds Jappelli) " what the import- 

 ance of learning how to take breath in running may be. How, if 

 this were determined by the quantity of blood circulating in 

 the capillary network of the bulb (deficit of 2 , increase of C0 2 ), 

 could it be modified by a physical education ? The polypnoea 

 of running is, however, mainly a luxus-respiration, an effect of 

 synchronisation, which represents a useless expenditure of energy, 

 and which, once the exigencies of the respiratory exchanges are 

 satisfied, may be modified for the sake of avoiding fatigue. The 

 education of respiratory rhythm in a runner therefore amounts to 

 developing in him an inhibitory cerebral faculty, so that he 

 moderates the frequency of his respiration, opposing the tendency 

 towards synchronisation with the movements of the lower limbs." 



X. Let us now examine whether in normal quiet respiration 

 (eupnoea) the respiratory activity is commensurate with the 

 quantity of oxygen required by the tissues, and the carbonic acid 

 which they exhale ; or if in this case also, as in the dyspnoea of 

 muscular work, the renewal of pulmonary air is in excess of what 

 is required, the nervous mechanisms of the respiratory rhythm 

 being to a certain extent independent of the gaseous content of 

 the blood circulating in them. 



Rosenthal in 1862 espoused the first theory on the strength of 

 a number of experiments, more particularly the phenomenon of 

 experimental apnoea, of which he may be termed the discoverer, 

 and which we shall consider below. His theory, broadly speaking, 



