262 



EXPERIMENTAL GENERAL SCIENCE 



and there along the lymphatic tubes are spongy bodies called 

 glands or nodes in which the white corpuscles are formed. The 

 glands also retard the passage of bacteria through them 

 and when an adjacent part is invaded by bacteria may be- 

 come swollen and tender to the touch. They are often called 

 kernels when noticed under the arms or about the throat. 



223. The Heart. The heart is a hollow, pear-shaped organ 

 composed of muscle, and is about the size of the fist. It is 

 located in the center of the thorax between the lungs, but 

 since the lower part is tipped somewhat to the left, the beating 



FIG. 90. White corpuscles penetrating capillary walls. 

 and Stirling.) 



(Landois 



is felt between the fifth and sixth ribs on the left side. The 

 heart has four chambers, two for pumping the blood and two 

 which act as receiving chambers for it as it returns to the 

 heart. The heart is suspended in the thoracic cavity and 

 the blood vessels connect with it at the upper side. It beats 

 or contracts rhythmically as long as the body is alive and gets 

 its rest for a short period between each beat. In infancy, the 

 heart beats about 140 times a minute, in youth the rate is 

 from 90 to 100 and in adult life it is from 70 to 75. These 

 pulsations may be felt in various parts of the body where the 



