6 HUMAN PHYSIOLOGY CHAP. 



some sugar and starch, fats, and salts. These little 

 masses are held in place by fine threads or fibers known 

 as connective tissue. 



Scrape the moist lip lightly with a knife and place the mass under 

 the microscope. Try to find very light, flat, irregular scales. These 

 are scaly cells. Make a drawing. 



8. Some Definitions. 



1. A cell is any mass of living matter containing a 

 nucleus. 



2. A tissue is a collection of similar cells having the 

 same functions, as bony tissue, nerve tissue, muscle 

 tissue, and fat or adipose tissue. 



3. An organ is a collection of several tissues arranged 

 in some definite and compact way to perform some 

 special function, as the heart, lungs, liver, and eye. 



4. A system is a group of several organs that aid 

 each other in doing the same kind of work, as the 

 nervous, muscular, and digestive systems. 



5. An organism is a collection of all the systems 

 necessary to carry on the life processes, as man, dog, 

 fish, and oyster. 



9. The Body compared to a City. A city consists of 

 hundreds of human beings all dependent upon one 

 another, each having his desires and wants and con- 

 tributing his share to the common good. Trains, boats, 

 and wagons are busy carrying food, fuel, and luxuries 

 to supply the needs and satisfy the wants of each 

 individual in the city. The city depends upon the 

 surrounding country, upon other cities, and more or less 

 upon the rest of the world. Water is piped into the 



