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130 Living Things Are Basically Alike uxn 11 



In studying the arm, you just read 

 about bone tissue, muscle tissue, nerve 

 tissue, blood tissue, gland tissue, fat tissue, 

 and epithelial tissue. 



Sometimes the cells making up a tissue 

 deposit some nonliving material around 

 themselves. This nonliving material is 

 called intercellular matter. The word 

 "intercellular" means lying between the 

 cells. Bone is a particularly good example 

 of cells that do this. The bone cells sur- 

 round themselves with a large amount of 

 mineral matter. This lifeless matter be- 

 comes an important part of the tissue; 

 the hardness and rigidity ^\•hich you as- 

 sociate with bone are due to the inter- 

 cellular matter. Some other tissues besides 

 bone have intercellular material, although 

 the relative amount of intercellular ma- 

 terial is smaller than in bone. Thus we 

 nmst add this new idea to our definition 

 of a tissue and say that a tissue is a group 

 of cells similar in structure and in work, 

 along with more or less intercellular ma- 

 terial which is produced by the cells. 



Tissues make up organs. You have read 

 of a number of tissues found in the arm. 

 But these same tissues are found in other 

 parts of the body as well. In general, 

 each tissue is found in many places 

 throughout a complex animal like a man 

 or a cat. And wherever the tissue is found 

 it is combined with other tissues, making 

 up a distinct part of the body known as 

 an organ. An organ is a part of the body 

 consisting of a group of tissues which 

 work together. The word organ must 

 not be mistaken for the word organism 

 which means a single living tiling or in- 

 dividual. The luart, the stomach, and 

 the liver are all internal organs of \-our 

 body. The skin may be considcrctl an 



Fig. 155 A small part of a bone, iiiaii^nijied. 

 Large dark spots are tubes contaming blood ves- 

 sels and nerves. S?nall dark spots are spaces 

 zvhere bone cells used to be. This tissue has in- 

 tercellular material, (richard st. clair) 



organ too, for it also consists of a group 

 of tissues which work together. You 

 read that a bone consists largely of bone 

 tissue but it has also nerve, blood, and 

 other tissues; it, too, may be considered 

 an organ. Often an organ does more than 

 one kind of work, or is useful to the 

 body in more than one way. P'or example, 

 the stomach not only helps in digestion 

 but it helps destroy harmful bacteria; 

 in it food is temporarily stored and it is 

 useful to the body in still other ways. 



Biologists often use the word function 

 (funk'shun) to refer to activities or 

 useful properties of organs, tissues, or 

 even single cells or parts of cells in an 

 organism. The stomach functions in di- 

 gesting certain kinds of food; protecting 

 other tissues from infection is one func- 

 tion of the skin; enabling a person to 

 hear is one function of the ears. To help 

 you understand this paragraph do Ex- 



KRCTSF, I. 



