VITAL FUNCTIONS 



456. Human Lungs and Heart. Fig. 96, represents 

 the Lungs, together with the Heart and large Arteries, and 



Fig. 96. 



Diaphragm as they are situated in man : , the Heart ; 

 b, b, the Lungs ; c, c, the Diaphragm. The bases of the 

 Lungs, it will be observed, rest upon the Diaphragm, 

 with which they are always in close contact. The Lungs 

 are distinguished into parts, called lobes, which are par- 

 tial divisions of their lower parts. The right side of the 

 chest being larger than .the left, because the Heart is 

 principally on the left side, the right Lung has three 

 lobes, while the left has only two. The Lungs are 

 entirely made up of air cells and blood vessels, inter- 

 mingling with each other in the closest manner, the two 

 fluids being divided from each other by the thinnest mem- 

 branes. Thus as the blood passes through the Lungs, it 

 is largely exposed to the influence of the air through this 

 membrane. 



457. Such is the extreme tenuity of these vessels, that 

 Dr. Keil estimated the number of cells in the Lungs to be 

 nearly 180 millions, and Dr. Hales, supposing each air- 

 cell at 1-100 part of an inch in diameter, computed 

 that the whole surface in both Lungs would be equal to 

 20,000 square inches. It is upon the surface that the 

 venous blood is distributed by an equal infinity of vessels, 

 and by which means it is aerated, or changed into 

 arterial blood* which is then immediately sent to reno- 

 vate and vivify the whole system, as shown in the de- 



What are the relative situation of the lungs, heart, and diaphragm ? 

 What is the substance of the lunes composed ol ? What amount of surface 

 is it computed the air vessels of the lungs contain ? 



