16 



THE HUMAN BODY. 



from the inside of the wall of the abdomen. Elsewhere 

 we find cells elongated, as c, Fig. 5 ; if this goes on to any 

 great extent we get a long slender thread which is called 

 &Jiber; but very often fibers are made by a number of 

 cells, all elongating a little and then 

 joining together end to end. Ex- 

 amples of fibers are shown in Figs. 35 

 and 85. Speaking in general terms, 

 we may say that the whole body con- 

 sists of tiny cells, either rounded and 

 thick, flat and thin, or elongated to 

 form fibers. Just as a wall is built 

 of distinct bricks or stones, so an 

 organ is made up of a number of cells. 

 All the solid parts of the body are 

 either cells or fibers which have grown 

 from cells, except something which corresponds pretty 

 closely to the mortar which lies between the bricks of a 

 wall and holds them together. This latter material, 

 known in the body as intercellular substance, is in some 

 places abundant, in others scanty or absent. 



Wherever found, the intercellular substance is made 

 by the cells which lie imbedded in it ; they pass it out 

 from their surfaces and repair it when necessary, and in 

 this respect it differs very essentially from the mortar 

 which a mason lays between his bricks. 



Summary. Cells are thus at bottom the things which 



FIG 6. Flat cells from 

 the surface of the lining 

 membrane of the abdo- 

 men ; a, cell body ; b, nu- 

 cleus; c, nucleoli. 



What are fibers ? How are they made ? In what respect may an 

 organ be compared to a brick wall ? What corresponds to the mortar 

 of the wall ? What makes tlie intercellular substance? How ? 



State briefly the relationship of its cells to the structure and work- 

 ing of the body. 



