534 VETERINARY PHYSIOLOGY 



geal branch of the vagus, the sensory nerve of the larynx, does 

 not alter the rhythm of respiration. Stimulation of the upper 

 end of the cut nerve causes first an inhibition of inspiration, 

 and, if stronger, produces forced expiratory acts. This is well 

 illustrated by the very common experience of the effect of a 

 foreign body, such as a crumb, in the larynx. The fit of cough- 

 ing that ensues is a series of expiratory acts reflexly produced 

 through this nerve. 



a 



(b) When the splanchnics in the abdomen are stimulated, 

 inspiration is inhibited. Every one has experienced the " loss 

 of wind " as the result of a blow on the abdomen. 



(c) The glossopharyngeal, which supplies the back of the 

 tongue, when stimulated, as by the passage of food in the act 

 of swallowing, causes an instant arrest of the respiratory move- 

 ments either in inspiration or expiration. The advantage of this 

 in preventing the food, as it is swallowed, from passing into the 

 trachea is obvious (fig. 216, d and d'). 



(d) Stimulation of the cutaneous nerves stimulates the in- 

 spiratory centre and causes a deep inspiration. This is seen 

 when cold water is dashed upon the skin. Stimulation of the 

 skin by slapping is sometimes used to establish breathing in the 

 newly born infant. The reaction is most clearly demonstrated in 

 animals with the vagi cut when an inspiratory movement may 

 often be liberated by merely touching the skin. 



3. Influence of Temperature. — The temperature of an animal 

 also acts on the respiratory centre. Increase in temperature 

 accelerates the rate of the heart and it also accelerates the rate 

 of the respirations in about the same proportion. This is seen 

 in feverish attacks, where pulse and respirations are proportion- 

 ately quickened so that their ratio remains unaltered. When 

 the respiratory rate rises out of proportion to the rate of the 

 pulse it is usually an indication that some pulmonary irritation 

 is present. 



4. Postural Control. — In diving birds the respirations are 

 controlled by a postural reflex from the labyrinths and neck. 

 When the head is put in the diving position respirations are 

 stopped. The respiratory centre in these birds does not respond 

 to the Ch of the blood, but rather to the want of oxygen. 



