CHAP. IL] RESPIRATION. 319 



FIG. 56. APPARATUS FOR TAKING TRACINGS OF THE MOVEMENTS or THE 

 COLUMN OF AIR IN RESPIRATION. 



The recording apparatus shewn is the ordinary cylinder recording apparatus. The 

 cylinder A covered with smoked paper is by means of the friction-plate B put into 

 revolution by the spring clock-work in C regulated by Foucault's regulator D. By 

 means of the screw E, the cylinder can be raised or lowered, and by means of the 

 screw F its speed may be increased or diminished. 



The tracheotomy tube t fixed in the trachea of an animal is connected by india- 

 rubber tubing a with a glass T piece inserted into the large jar G. From the other 

 end of the T piece proceeds a second piece of tubing b, the end of which can be either 

 closed or partially obstructed at pleasure by means of the screw clamp c. From the 

 jar proceeds a third piece of tubing d, connected with a Marey's tambour TO (see 

 Fig. 22, p. 140), the lever of which I writes on the recording surface. When the tube 

 b is open the animal breathes freely through this, and the movements in the air of 

 G and consequently in the tambour are slight. On closing the clamp c, the animal 

 breathes only the air contained in the jar, and the movements of the lever of the 

 tambour become consequently much more marked. 



Below the lever is seen a small time-marker n connected with an electro-magnet, 

 the current through which coming from a battery by the wires x and y is made and 

 broken by a clock-work or metronome. 



In what may be considered as normal breathing, the respiratory 

 act is repeated about 17 times a minute ; and the duration of the 

 inspiration as compared with that of the expiration (and such pause 

 as may exist) is about as ten to twelve. 



The rate of the respiratory rhythm varies very largely, and in 

 this as in the volume of each breath it is very difficult to fix 

 a satisfactory average, the figures given varying from 20 to 13 a 

 minute. It varies according to age and sex. It is influenced by 

 the position of the body, being quicker in standing than in lying, 

 and in lying than in sitting. Muscular exertion and emotional 

 conditions affect it deeply. In fact, almost every event which 

 occurs in the body may influence it. We shall have to consider in 

 detail hereafter the manner in which this influence is brought to 

 bear. 



When the ordinary respiratory movements prove insufficient to 

 effect the necessary changes in the blood, their rhythm and 

 character become changed. Normal respiration gives place to 

 laboured respiration, and this in turn to dyspnoea, which, unless 

 some restorative event occurs, terminates in asphyxia. These 

 abnormal conditions we shall study more fully hereafter. 



The Respiratory Movements. 



When the movements of the chest during normal breathing are 

 watched, it is seen that during respiration an enlargement takes 

 place in the antero-posterior diameter, the sternum being thrown 

 forwards, and at the same time moving upward. The lateral width 

 of the chest is also increased. The vertical increase of the cavity 

 is not so obvious from the outside, though when the movements of 



