CHAP, ii.] RESPIRATION. 431 



of Fick is somewhat similar. Or changes in one or other diameter 

 of the chest may be recorded by what may be called the ( callipers' 

 method, as in the recording stethometer of Burdon-Sanderson. This 

 consists of a rectangular framework constructed of two rigid parallel 

 bars joined at right angles to a cross piece. The free ends of the 

 bars, the distance between which can be regulated at pleasure, are 

 armed, the one with a tambour, the other simply with an ivory 

 button. The tambour bears on the metal plate of its membrane 

 (m' Fig. 36) a small ivory button in place of the lever. When it is 

 desired to record the changes occurring in any diameter of the chest, 

 e.g. an antero-posterior diameter from a point in the sternum to a 

 point in the back, the instrument is made to encircle the chest some- 

 what after the fashion of a pair of callipers, the ivory button at one 

 free end being placed on the spine of a vertebra behind and the 

 tambour at the other on the sternum in front in the line of the diam- 

 eter which 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 con- 

 veyed 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 

 callipers 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 pericardial cavity, a cannula connected 

 by a rigid tube with a manometer. With each inspiration a nega- 

 tive 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 oesophagus an elastic sound (similar 

 to the cardiac sound Fig. 36) connected with a tambour. The 

 oesophagus 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 move- 

 ments. 



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 inspi- 

 ration 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 



