THE RESPIRATORY MECHANISM. 397 



draw blood into it. Since the normal heart has muscular 

 power, and to spare, for its systole, this arrangement, by 

 which some of the work then spent is stored away to assist 

 the diastole, which cannot be directly performed by cardiac 

 muscles, is of service to it on the whole. It is a physiological 

 though not a mechanical advantage; no work power is 

 gained, but what there is, is better distributed. 



Influence of the Respiration on the Lymph-Flow. 

 During inspiration, when intra-thoracic pressure is lowered, 

 lymph is pressed into the thoracic duct from the abdominal 

 lymphatics. In expiration, when thoracic pressure rises 

 again, the extra lymph cannot flow back on account of the 

 valves in the lymphatic vessels, and it is consequently driven 

 on to the cervical ending of the thoracic duct. The breath- 

 ing movements thus pump the lymph on. 



