THE LIVING MATERIAL OF THE BODY 



11 



are thus distinct subjects, yet so closely related that they 

 will be considered separately. 



ORGANS AND TISSUES 



There are several familiar fundamental facts concerning 

 living things; everyone knows that the commoner animals 

 feed, breathe, feel, give off waste material, have blood 

 circulating through their bodies and show many ether points 

 of similarity. It may, however, surprise some people to learn 

 that these same functions are carried on in 

 plants, for they, too, must feed, breathe, give off 

 waste and have some kind of circulatory system, 

 although, to be sure, these life processes occur 

 differently in animals' and plants. An organism 

 is anything which carries out the functions of 

 life. 



Certain very important differences exist be- 

 tween the lower (i.e. microscopic) organisms and 

 the higher ones. In many of the lower types 

 of animal and plant life all parts of the body 

 may perform the same office, e. g. of loco- 

 motion, sensation or feeding; but it is apparent 

 to anyone that different parts of the human 

 body such as heart, stomach, brain or eye, per- 

 form each its own work or function ; and each is 

 therefore called an organ. An organ may be 

 defined as a part of the body which has one special 

 kind of work to do. This work as a rule contri- 

 butes to the sustaining of every other part of the 

 organism. The whole body, then, may be pictured as com- 

 posed of many separate and distinct organs, each cooperat- 

 ing with the other and thus constituting one organism. 

 Even the microscopic animals, like those in Figure 1, have 

 some very simple organs, as for instance, the nucleus shown 

 at N. 



FIG. 1 . Hy- 



ALODISCUS 

 LIMAX 



A microscopic 

 animal resem- 

 bling amreba, 

 which lives in 

 fresh water. 

 All parts of 

 the body are 

 nearly alike 

 and perform 

 the same 

 functions. N 

 is the nucleus. 



