GENERAL BUILD OF THE HUMAN BODY 



,9 



There are other organs, called the excretory organs, which 

 perform the office of removing certain impurities from the blood as 

 it circulates through them. The chief of these organs are the 

 liver, the kidneys, and the skin ; to which may also be added the 

 lungs ; for, in addition to being aerated, the blood, while in the 

 lungs, is caused to give up a gas called carbonic-acid gas, which it 

 has collected in its passage through the various parts of the body. 



The liver is a very large reddish-brown organ, which prepares 

 a substance called bile from the blood. Although the separa- 

 tion of bile may be re 

 garded as a process of 

 blood - purification, yet 

 the bile itself is utilised 

 in the digestion of food. 

 The liver, therefore, is 

 not simply an excre- 

 tory organ, but may 

 also be said to belong 

 to the digestive system. 



The kidneys, two 

 in number, are im- 

 portant blood-purifiers. 

 They separate a poison- 

 ous substance called 

 urea from the blood. 



The skin, which en- 

 tirely covers the exterior 

 surface of the body, is 

 more than a mere pro- 

 tective covering, for its 

 deeper layer contains 

 numerous small bodies, 

 in which a process of 

 blood - purification is 

 carried on, the impu- 

 rities separated being 



conducted by minute tubes to the pores or openings 

 may be seen with a lens on the surface of the skin. 



The nervous system consists of two parts. One of these is 

 called the cerebro- spinal system, and the other the sympathetic or 

 ganglionic system. The cerebro-spinal system consists of the 

 brain and the spinal cord, together with the numerous nerves 

 which proceed from these organs to almost all parts of the body. 

 The sympathetic system (see fig. 1 6 1) consists of a large number of 

 small masses of nerve substance (ganglia), and the nerves connect- 



Fig. 7. Front View of the Larynx, Trachea, 

 and Lungs. 



i, larynx ; 2, trachea ; 3, lungs. 



which 



