RESPIRATORY ORGANS. 99 



CONVERSATION V. 



Respiration the lungs the thorax mechanism of 

 inspiration changes wrought on the air by respiration 

 relation of these changes to those wrought on the 

 blood animal heat respiration of Fishes of Birds 

 of Reptiles of Mollusca and Insects of Spiders. Se- 

 cretion various kinds of Secretions Secretion in the 

 inferior animals. Jfbsorbtion performed chiefly by the 

 veins the lymphatics the lymph. Nutrition. 



Dr. B. To day we are to consider the changes which 

 the blood undergoes in its passage through the lungs, 

 and the mechanism of the parts concerned in producing 

 them. The respiratory organs are two light, spongy, 

 and rather irregularly shaped bodies, placed in the tho- 

 rax, or chest, one on each side, called the Lungs.-^- 

 They are composed almost entirely of air-cells and 

 blood vessels, though some other tissue is probably pre- 

 sent, which serves as a common bond of union. These 

 little air-cells, which are of extreme minuteness, are 

 distributed to every portion of the organ, and seem to 

 be the ultimate ramifications of two large tubes, which 

 lead, one to each lung, called the bronchiae. The blood 

 vessels belong to the capillary system, and communicate 

 with the pulmonary arteries and veins. They are 

 situated in the tissue of the cells, and it is while the 

 blood is passing through them, that it is subjected to 

 the respiratory process. The bronchiae are the subdi- 

 visions of a single tube, called the trachea, or windpipe. 



