22 ELEMENTARY PHYSIOLOGY less. 



bodily framework are competent to be affected, in such a 

 manner as to cause the sensations of taste or of smell, of 

 sight or of hearing: and 'only a few substances, or par- 

 ticular kinds of vibi-ations, are able so to affect those 

 regions. These very limited parts of the body, which put 

 us in relation with particular kinds of substances, or forms 

 of force, are what are termed sensory organs. There 

 are two such organs for sight, t^vo for hearing, two for 

 smell, and one, or more strictly speaking two, for taste. 



And now that we have taken this brief view of the 

 structure of the body, of the organs which support it, of 

 the organs which move it, and of the organs which put it 

 in relation with the surrounding world, or, in other words, 

 enable it to move in harmony with influences from with- 

 out, we must consider the means by which all this Avonder- 

 ful apparatus is kept in working order. 



All work, as we have seen, implies waste. The work 

 of the nervous system and that of the muscles, therefore, 

 implies consumption either of their own substance, or of 

 something else. And as the organism can make nothing, 

 it muse possess the means of obtaining from without that 

 which it wants, and of throwing off from itself that which 

 it wastes ; and we have seen that, in the gro.ss, it does 

 these things. The body feeds, and it excretes. But we 

 must now pass from the broad fact to the mechanism 

 by which the fact is lirought about. The organs wdiich 

 convert food into nutriment are the organs of alimenta- 

 tion ; those which distribute nutriment all over the 

 body are organs of circulation ; those which get rid of 

 the waste products are organs of excretion. 



7. Alimentary Organs. — The organs of alimentation 

 are the mouth, pharynx, gullet, stomach, and intestines, 

 with their appendages. What they do is, first to receive 

 and grind the food. They then act upon it with chemical 

 agents, of which they ])o.ssess a store which is renewed as 

 fast as it is used ; and in this way convert the food by 

 processes of digestion into a fluid containing nutritious 



