INTRODUCTION 



THE science which treats of the structure, function and organi- 

 zation of living forms, both vegetable and animal, is called 

 biology. That branch of biology which describes animal life 

 exclusively is termed zoology, while that branch which de- 

 scribes vegetable life exclusively is termed botany. 



The study of the form of organisms, both vegetable and 

 animal, is termed morphology. Morphology is further divided 

 into (i) histology, which treats of the formed elementary con- 

 stituents of organisms, and (2) anatomy, which treats of the 

 parts and organs of the organism. 



After the form and structure of an organism has been studied, 

 the next step is the study of the work which the organism has 

 to perform. This study of the vital phenomena, or life, of the 

 organism is called physiology. Physiology may be either 

 animal or vegetable. Human physiology is that branch of 

 physiology which treats of the vital phenomena occurring in 

 man. 



The structural unit of the body is the cell. Myriads of cells 

 are grouped together to form organs. An organ may be denned 

 as a group of cells combined together to perform some special 

 function, e. g., the kidney is an organ whose special function is 

 the secretion of urine. The organs are further grouped together 

 to form systems. Thus we have the circulatory system com- 

 posed of the heart, arteries, veins, and capillaries. Now the 

 study of the function which the circulatory system has to per- 

 form is the physiology of circulation. Likewise we may sub- 

 divide physiology into the physiology of the nervous system, 



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