RESPIRATION. 143 



body are freely separated, and the new and vitalized ones 

 take their places, and the former are carried rapidly away, 

 and life is frequently renewed, and vigorously sustained. 

 But when the system is feeble and languid, when it is fever- 

 ish and generally disturbed, when it is exhausted by fa- 

 tigue or want of sleep, the reverse happens ; the circulation 

 is languid, the nutrition feeble, absorption slow, and a smaller 

 proportion of carbon and hydrogen is carried off. 



320. The system is relieved of these dead matters, more or 

 less, according to the condition of the lungs, in proportion 

 as they are healthy or unhealthy. In some diseases, their 

 texture is changed from an exceedingly porous and spongy 

 body, to one partially or entirely solid. In consumption, 

 a part of these organs is filled with tubercles, or abscesses. 

 Sometimes these occupy almost the whole substance of the 

 lungs, and leave so little room for air that respiration can- 

 not be carried on. Then the sufferer literally dies for want 

 of breath, because the lungs cannot receive sufficient air to 

 purify as much blood as is necessary to sustain life. The 

 impure blood which cornes to the lungs, to exchange its car- 

 bon for oxygen, does not find air to give it relief, and goes 

 back to the heart nearly as corrupt as when it came out. 



321. In lung fever, and some other diseases, a portion of 

 the lungs becomes solid, like liver, and the air-cells are 

 closed. If the whole of the lungs becomes consolidated, 

 death must follow ; but this state more frequently prevails in 

 a part only of these organs ; then the blood is sent back in an 

 imperfect condition, and the frame is then only partially nour- 

 ished. Some have sustained life for a considerable period 

 with only one sound lung ; but theirs was a feeble and lower 

 life, and they could not perform all the work, nor enjoy all 

 the comforts, of ordinary well-sustained existence. 



322. The states of the mind and feeling, as well as those 

 of the body, affect the discharge of waste matters through 

 the lungs. Cheerfulness and exhilaration, and the exciting 

 passions, increase the separation of carbon ; while the de- 

 pressing emotions fear, grief, and anxiety diminish it. 



