184 UNCONSCIOUS NERVOUS OPERATIONS 



259. The Lungs are made up of collections of air cells 

 and the branches of the bronchial tubes. Their texture 

 is spongy and elastic, and a piece of a lung, unlike 

 any other tissue, will float in water. Each lung is envel- 

 oped in the pleura, which is a serous membrane folded 

 back to form the lining of the diaphragm and the chest 

 wall. The two layers of the pleura are in contact with 

 each other, with only enough of the fluid secretion to 

 enable them to glide smoothly over each other. Each 

 lung is partly divided into lobes, there being three lobes 

 in the right and two in the left lung (Fig. 86). Each lobe 

 is also made up of many small parts called lobules, each con- 

 taining a minute branch of a bronchial tube with air cells, 

 blood vessels, nerves, and lymphatics. The air cells in 

 the different lobules have no communication with one an- 

 other, so that if one of the bronchial tubes is obstructed 

 the cells opening into it are not supplied with air. 



260. Blood supplied to the Lungs. The blood conveyed 

 to the lungs is from two sources: (1) The pulmonary 

 artery from the right ventricle brings the impure blood, 

 collected by the veins throughout the body, to be purified, 

 or oxygenated. (2) The bronchial arteries bring pure 

 arterial blood for the nutrition of all parts of the organ. 

 This is returned through the bronchial veins, and in some 

 measure also through the pulmonary veins. 



261. Inspiration and Expiration. The thorax is a closed 

 cavity, and the air cannot reach the outside of the lungs, 

 hence the pressure of the weight of the atmosphere affects 

 the lungs only from the inside, and they are kept dis- 

 tended to fill the cavity. If the thorax is increased in 

 size, the air rushes in and distends the elastic cells of the 

 lungs still more. If the cavity of the thorax is reduced 

 in size, the air is forced out, and the lungs are contracted. 



