CHAP, ii.] RESPIRATION. 541 



of its membrane (m' Fig. 37) 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 somewhat 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 

 diameter 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 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 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 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 resophagus an elastic sound (similar to the cardiac sound 

 Fig. 37) connected with a tambour. The oasophagus 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 enlarge- 

 ment 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 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 blood- 



