308 



SEROUS MEMBRANES. 



fected during the recession of the lung. Lying as this does in front of 

 the primarily affected spot, it will advance beyond this during the next 

 inspiration, and will accordingly contaminate a fresh portion of the 

 healthy parietal pleura {ft, 7) ; in a word, with each breath the patient 

 takes, a new zone, both of the parietal and the pulmonary pleurae, must 

 become contaminated. The extension of the irritant matter however, 

 occurs with varying rapidity in the various regions of the pleural sac. 

 It hardly amounts to anything in the neighbourhood of the apex and 

 the posterior border, and increases in proportion to its distance from 

 these points, reaching its maximum close to the free borders. 



The circumstances are somewhat modified in the case of the peri- 

 Btaltic movements of the bowels. At the moment when a segment of 



Tlie same at the end of expiration. References as before, 

 a, ft, y, see text. 



For 



intestine begins to take part in the wave of contraction passing from 

 above downwards along the circular fil3res, it forms, in conjunction with 

 the neighbouring segment which is already undergoing dilatation, an 

 inclined plane, surrounding the entire bowel. Upon this plane the 

 general pressure which exists in the abdominal cavity, breaks up into 

 two components ; the one, acting at right angles to the axis of the 



