532 



VETERINARY PHYSIOLOGY 



limitation of the free supply to the tissues of the oxygen which 

 has been taken up by the blood. This has been called Cheyne- 

 Stokes breathing (fig. 214). 



2. Reflex Regulation- 



The respiratory centre is also acted upon by various ingoing 

 nerves. 



(1) The Vagus. — Since the vagus is the ingoing nerve of the 

 respiratory tract, we should expect it to have an important 

 influence on the centre (fig. 215). 



Section of one vagus generally causes the respirations to 

 become slower and deeper ; but, after a time, the effect wears 



D^ap/2 



Fig. 215. — Nervous Mechanism of Respiration. B.C., respirator}' centre; 

 Citt., cutaneous nerves ; Ph., phrenics ; In.C, intercostal nerves ; P., 

 pulmonary branches of vagus ; S.L., superior laryngeal branch of 

 vagus; La., the larynx; G.Ph., glossopharyngeal nerve; Diaph., 

 diaphragm. 



off and the previous rate and depth of respiration are regained 

 (fig. 216). 



Section of both vagi causes a very marked slowing and 

 deepening of the respiration, which persists for some time, and 

 passes ofi" slowly and incompletely. But if, after the vagi 

 have been cut, the connection of the respiratory centre with 

 the upper brain tracts is severed, the mode of action of the 

 centre changes. Instead of discharging rhythmically, it may 

 discharge irregularly (fig. 216, c). 



To investio-ate further this influence of the vao;us it is neces- 

 sary to study the effect of stimulating the nerve. 



Strong stimulation of the pulmonary branches of one 



