ELEMENTS OF PHYSIOLOGY 



PART I. INTRODUCTORY KNOWLEDGE 

 CHAPTER I 



THE SKIN 



1. The skin that covers our bodies is elastic and in this 

 respect is like India rubber. But if they are both exam- 

 ined under the microscope, a marked difference is found. 

 Rubber resembles oil and water in being alike in all its 

 parts, while the skin is composed of an immense number 

 of small objects fitting together. Hence it is said to 

 have a definite structure, while rubber has not. These 

 small objects are called cells and fibers: fibers are usually 

 thread-like, while cells are of various shapes. In another 

 chapter it will be learned that each cell has life and activity 

 of its own, and that the fibers are believed to be branches 

 from the cells. A number of cells or a number of fibers, 

 or both together, make what is called a tissue. The tissues 

 form organs. An organ is a part of the body that has 

 special work to perform and this work is called its function. 

 The skin is an organ and its chief function is to protect 

 the body. Name the organ of sight. What is the function 

 of the teeth ? A number of organs working together for a 

 similar end is called a system. Thus the organs which 

 prepare the food constitute the digestive system ; those 

 which circulate the fluids, the circulatory system. 



2. The skin consists of two layers (Fig. i), the outer 

 layer, or epidermis, resting on the inner layer, the dermis, 



B i 



