338 RESPIRATION. 



is being studied. The distance between the free ends of the instrument being 

 carefully adjusted so that the button of the tambour presses lightly on the sternum, 

 any variations in the length of the diameter in question will, since the framework 

 of the tambour is immobile, give rise to variations of pressure within the tambour. 

 These variations of the "receiving" tambour, as it is called, are conveyed by a 

 flexible tube containing air to a second or ''recording'' tambour, the lever of 

 which records the variations on a travelling surface. For the purpose of measuring 

 the extent of the movements the instrument must be experimentally graduated. 

 Other forms of calipers may, of course, be used. 



By still another method the variations in intra-thoracic pressure, by means of 

 which the movements of the chest walls produce the movement of air in the 

 lungs, may be recorded. This may be effected by introducing carefully, to the 

 total exclusion of air, into a pleural cavity or into, the pericardia! cavity, a canula 

 connected by a rigid tube with a manometer. With each inspiration a negative 

 pressure, or rather an increase of the existing negative pressure, is produced, the 

 mercury, or fluid, in the manometer returning at each expiration. An easier 

 method of recording this intra-thoracic pressure is to introduce into the ossophagus 

 an ehstic sound (similar to the cardiac sound, Fig. 54) connected with a tambour. 

 The O3sophagus within the thorax, like the heart and great vessels, as we shall see, 

 is affected as well as the lungs by the variations of intra-thoracic pressure brought 

 about by the respiratory movements. 



In yet another method the movements of the diaphragm, which, as we shall see, 

 serve as the prime agent in bringing about the enlargement of the thoracic cavity, 

 are recorded. This may be done by inserting, through an incision in the abdominal 

 wall, a flat elastic bag between the diaphragm and abdominal organs. When in 

 inspiration the diaphragm descends, it exerts on the bag a pressure which, by 

 means of a tube, may be communicated to a tambour. Or a needle may be thrust 

 through the chest wall so as to rest upon or transfix the diaphragm, and the head 

 of the needle outside the body connected by a thread or otherwise with a lever ; each 

 upward and downward movement of the head of the needle, corresponding to the 

 downward and upward movements of the diaphragm, is registered by the lever. 



Various modifications of these several methods have been adopted by various 

 observers. They all, however, leave much to be desired. A very ingenious method 

 of registering the contractions of the diaphragm has recently been introduced. In 

 the rabbit two slips of muscular fibres forming part of the diaphragm, one on each 

 side of the ensiform cartilage, are so disposed and possess such attachments that 

 one or both of them may be isolated without injury to either nerves or bloodvessels, 

 and arranged so that while one end of the slip is securely fixed to the chest-wall as 

 a fixed point, the other end can by a thread be brought to bear on a lever. The 

 slip, even when thus arranged, appears to contract rhythmically in complete unison 

 with the contractions of the whole of the rest of the diaphragm : it serves, so to 

 speak, as a sample of the diaphragm ; and hence its contractions, like those of the 

 whole diaphragm, may be taken as a record of respiratory movements. The record 

 has to be corrected for variations in the position of the fixed point. 



272. In these various ways curves are obtained, which, while differing 

 in detail, exhibit the same general features, and more or less resemble the 

 curve shown in Fig. 91. 



As the figure shows, inspiration begins somewhat suddenly and advances 

 rapidly, being followed immediately by expiration, which is carried out at 

 first rapidly, but afterward more and more slowly. Such pauses as are seen 

 usually occur between the end of expiration and the beginning of inspira- 



uro by means of the screw clamp c. From the jar proceeds a third piece of tubing d, connected 

 with a Marey's tambour m (see Fig. 54), 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 conse- 

 quently 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. 



