1879.] concerned in the Abdominal Circulation in Man. 493 



In computing the effect of the descent of the diaphragm we must 

 always bear in mind the effect of the expansion of the lower part or 

 base of the thorax ; for this by lifting off as it were the pressure of 

 the abdominal muscles attached to it from the viscera beneath, lessens 

 the effect of the descent of the diaphragm. Notwithstanding this 

 there is a notable residuum of force. 



The effect of expiration on the abdominal circulation would be pro- 

 bably to gradually permit a restitution of the balance interfered with. 

 The elasticity of the walls would sustain, to a considerable degree, the 

 pressure ; the portal vein and vena cava would gradually accumulate 

 blood, and this in coincidence with an increment in that of the superior 

 cava and right cavities of the heart till the irritation of its presence 

 causes another inspiratory act. 



It may be noticed that the tension of the arterial pulse would 

 be naturally increased during the expansion of the lungs, because 

 of the greater supply of blood to the left half of the heart shortly after 

 the commencement of the inspiration, and thus the resistance to the 

 flow of venous blood through the lung capillaries is lessened ; and this 

 action it is impossible to ignore when we are discussing the effect of 

 the incipient vacuum on the venous blood-pressure during inspiration. 



The same method of registering the effect of the respiratory move- 

 ments on the abdomen also is applicable to marking the effects of the 

 general movements of the body. The elevation of the arm or the leg, 

 coughing and laughing, &c, are easily seen to compress the abdomen. 



It would be beside the intention of this note to discuss the manner 

 in which this effect of movements of the body is produced ; but I may 

 point out that in the act of coughing and laughing we have, as indeed 

 might be expected, evidence not only of high pressure (shown by the 

 sudden elevation of the wave), but also a tendency to vacuum, as 

 illustrated by the sudden descent of the wave below the line. 



These actions must tell violently on the blood- current of the abdo- 

 men, and tend to force it out of this cavity ; and, as before remarked, 

 the resultant of this must be to facilitate the current in its normal 

 direction. The same effect must be produced on the other fluids in 

 the abdomen, and must assist the movement of the secretions contained 

 in the ducts of the various organs, notably that of the liver. 



(Received April 16.) 



In the foregoing note no calculation has been made as to the 

 amount of the forces produced by the descent of the diaphragm in 

 ordinary respiration. Its extreme violent action has been calculated 

 by Professor Haughton at 20 lbs. on the square inch ; but the amount 

 of pressure on the contents of the abdomen must vary much, accord- 

 ing to the resistance exerted by the parietes. When the intestines are 

 empty of gaseous contents, and the previously over-distended abdomen 



VOL. xxviii. 2 o 



