432 



RESP1KATORY CUKVES. 



[BOOK ii. 



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 dia- 

 phragm 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 contractions of the whole rest of the diaphragm ; it serves 

 so to speak as a sample of the diaphragm ; and hence its contrac- 

 tions like those of the whole diaphragm may be taken as a record 

 of respiratory movements. The record has to be corrected for vari- 

 ations in the position of the fixed point. 



260. 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. 86. 



FIG. 86. TRACING OF THORACIC RESPIRATORY MOVEMENTS OBTAINED BT 

 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 ft, and expiration from b 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 expira- 

 tion, 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. As we shall see in detail hereafter, 

 the several parts of the whole act vary much, under various cir- 

 cumstances, in relation to each other. Sometimes expiration, 

 sometimes inspiration is prolonged; and either inspiration 



