CHAP, ii." 



RESPIRATION. 



571 



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 

 vessels, 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 con- 

 tractions of the whole 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. 



329. In these various ways curves are obtained, which, while 

 differing in detail, exhibit the same general features, and more or 

 less resemble the curve shewn in Fig. 72. 



FIG. 72. 



TRACING OF THORACIC EESPIRATORY MOVEMENTS OBTAINED BY 

 MEANS OF MAREY'S PNEUMOGRAPH. 



A whole respiratory phase is comprised between a and a; inspiration, during which 

 the lever descends, extending from a to 6, and expiration from 6 to a. The 

 undulations at c are caused by the heart's beat. 



As the figure shews, inspiration begins somewhat suddenly and 

 advances rapidly, being followed immediately by expiration, which 

 is carried out at first rapidly, but afterwards more and more 

 slowly. Such pauses as are seen usually occur between the end of 

 expiration and the beginning of inspiration. In normal breathing, 

 hardly any such pause exists,, but in cases where the respiration 

 becomes infrequent, pauses of considerable length may be observed. 



OF THE 



