422 



PHYSIOLOGY 



CHAP. 



Next to the respiratory movements of the vocal cords come 

 those of the nostrils, which are essentially analogous with the 

 first, and also appear regularly in man, in a certain number of 

 cases, while in some animals (e.g. rabbit) they are never wanting, 

 and in others (e.g. the horse) they play a very important part, 

 paralysis of the corresponding muscles being apt to produce 

 suffocation. They consist in the expansion of the nostrils, 

 coincident with inspiration (or more accurately, commencing just 

 before the phase of inspiration proper), and a subsequent constric- 



FIG. 187. Apparatus for registering respiratory movements of an animal by the oscillations of 

 pressure in the respiratory passages. X, Hutchinson's spirometer, to which is attached a 

 small metal pointer rf which records the oscillations of pressure in the animal's trachea 

 upon the smoked drum ; R, large receiver from which the animal breathes, connected by 

 to spirometer, by b to the trachea. The tube c permits more or less rapid renewal of air 

 in receiver, according as the lumen is mere or less constricted. 



tion, which coincides more or less exactly with the expiratory 

 phase. 



In forced respiration (dyspnoea) these concomitant respiratory 

 movements occur, as we have seen, to an exaggerated degree, even 

 in individuals in whom they are not observed in normal quiet 

 respiration. Other movements are then associated with them, e.g. 

 foaming at the mouth, protrusion of the tongue, etc., etc., showing 

 that the object is to give free access of air to the respiratory 

 passages. 



VIII. Ventilation or the renewal of the pulmonary air, effected 

 by the alternate movements of dilatation and contraction of the 

 thorax, varies in proportion to the varying intensity of these move- 

 ments. The name of tidal air is given to the volume of air which 



