RECORDING RESPIRATORY MOVEMENTS 257 



tion of the chest walls, therefore, admirably adapts them for recoiling against 

 and resisting as well undue contraction as undue dilatation. 



Respiratory Movements of the Nostrils and of the Glottis. During 

 the action of the inspiratory muscles which directly draw air into the chest, 

 those which guard the opening through which the air enters are also active. 

 In hurried breathing the dilatation of the nostrils is well seen, although 

 under ordinary conditions it may not be noticeable. The opening at the 

 upper part of the larynx, however, the rima glottidis, is dilated at each in- 

 spiration for the more ready passage of air, and becomes smaller at each 

 expiration; its condition, therefore, corresponds during respiration with 

 that of the walls of the chest. There is a further likeness between the two 

 acts in that, under ordinary circumstances, the dilatation of the rima glot- 

 tidis is a muscular act and its contraction chiefly an elastic recoil; although, 

 under various special conditions to be hereafter mentioned, there may be 

 considerable muscular contraction exercised. 



Methods of Recording Respiratory Movements. The movements of respiration 

 may be recorded graphically in several ways. The ordinary method is to introduce a 

 tube into the trachea of an animal, and to connect this tube by some gutta-percha tubing 

 with a T-piece, the side branch of which is connected with a Marey's tambour, which may 

 be made to write on a recording surface, figure 173. If the tube attached to the free limb 

 of the T-piece be partially closed with a screw compress, the movements of inspiration 



FIG. 23 1 . Stethogr-vph or P -eumograph. h. Tambour fixed at right angles to plate of steel, f ; 

 c and d, arms by which i strument is attached to chest by belt, e. When the chest expands, the 

 arms are pulled asunder, which bends the steel plate, and the tambour is affected by the pressure of 

 6, which is attached to it on the one hand, and to the upright in connection with horizontal screw, g. 

 (Modified from Marey's instrument.) 



and expiration are larger than if it were open. The alteration of the pressure within the 

 lungs on inspiration and expiration is shown by the movement of the column of air in the 

 trachea and in its extension to the T-piece. By these means a record of the respiratory 

 movements may be obtained. 



Various instruments have been devised for recording the movements of the chest 

 by application of apparatus to the exterior. Such is the stethometer of Burdon-Sanderson, 

 figure 233. This consists of a frame formed of two parallel steel bars joined by a third 

 17 



