456 PHYSIOLOGY CHAP. 



produces a passive rise of the abdominal wall, and thus drives the 

 air out of the trachea. Active thoracic expiration is immediately 

 succeeded by passive inspiration, in which the thorax rises again,- 

 and the abdomen falls. 



These exceptional phenomena, with the cause of which we are 

 unacquainted, and which accordingly cannot be determined 

 experimentally, have no physiological significance other than that 

 of showing the existence of an expiratory centre, which can 

 function separately when the inspiratory centre is put out of court. 

 Moreover, these and other facts investigated by Aducco show that 

 in the dog forced expiration is no functional unity, effected always 

 in the same way, and by the help of the same mechanism. It 

 may be carried out by the walls of the thorax or by the walls of 

 the abdomen. In the abdomen itself, according to Aducco, it is 

 possible to separate two expiratory mechanisms the interior recti, 

 and the lateral muscles. These different expiratory mechanisms 

 (thoracic, and anterior and lateral abdominal) may function 

 simultaneously or synchronously or simultaneously and a- 

 synchronously, or lastly, separately from one another. 



Other similar phenomena, noted incidentally by various 

 authors (Hering and Breuer, Luciani, Stefani, and Sighicelli, &c.), 

 but which Mosso (1878-1885) specially emphasised, show that the 

 inspiratory centre, too, may be regarded as an aggregate of centres, 

 which, although they normally function harmoniously, while each 

 retains a certain degree of autonomy and independence, may yet, 

 under certain indefinable conditions, come into play at different 

 times, act with unequal intensity, and even be capable of func- 

 tioning separately. According to Mosso, we must at any rate 

 accept a facial, a thoracic, and a diaphragmatic centre for inspira- 

 tion, since on comparing the simultaneous tracings from the three 

 different groups of muscles, a-synchronisms or different intensities 

 of action can be detected at different times upon the same 

 individual. The most striking fact of this kind is that in sleep 

 respiration is essentially costal, since (as shown in another con- 

 nection, Fig. 184, p. 418) the diaphragm is virtually inactive. In 

 the death-agony, on the contrary, the opposite prevails ; only the 

 'diaphragm is active, while the intercostal muscles are paralysed. 

 We must conclude that in sleep the thoracic and diaphragmatic 

 inspirations coincide, the first, however, outlasting the second : at 

 other times thoracic inspiration precedes the diaphragmatic. 



From these and other similar facts Mosso concluded that " the 

 earlier conception of a single respiratory centre must be abandoned ; 

 the respiratory movements of the facial muscles, diaphragm, 

 thorax, and abdomen have their specific nerve centres, which 

 function autonomously." Schiff, in his last work (1894), criti- 

 cised this attempted decentralisation of respiratory innervation. 

 According to him the special centres of the spinal cord, on which 



