4 HUMAN BIOLOGY 



attach the muscles to the bones. If we run a clean needle 

 point into the finger, blood flows ; in this way we discover 

 another of the materials found in our hand ; namely, blood. 

 This experiment also demonstrates that the human body has 

 some structures by the help of which sensations of touch or 

 pain are perceived. All the parts of the hand we have been 

 enumerating are known as tissues. For the present a tissue 

 may be defined as one of the building materials of which an 

 organ is composed. In the hand we have found evidence of 

 the presence of bone tissue, muscle tissue, connective tissue, 

 blood tissue, and nerve tissue. Other kinds of tissue will be 

 discussed in the pages that follow. 



In order to go farther m our study of structure we need 

 the aid of the compound microscope. With this instrument 

 we discover that the tissues are by no means the simplest 

 part of an animal. 



4. Cells lining the mouth. — Laboratory study. 



Materials : Cells from the human body may be readily prepared 

 by gently scraping with the finger nail the mucous membrane 

 hning the mouth and then rubbing the material thus obtained on a 

 clean glass slide, adding a drop of water and a cover glass. The 

 cells may be stained with iodine in order to show the nucleus more 

 sharply. If time allows, prepared sections of the brain, intestines, 

 skin, and other organs of the body may well be shown. 



Examine with the low power of the compound microscope 

 the cells prepared as described above. 



1. Describe the form and color of each cell before it is 



stained with iodine. 



2. In the cells stained with iodine notice a body, usually near 



the center, that is more deeply stained than the rest 

 of the cell. This is the cell nucleus, and the rest of 

 the cell is known as the cell body. The nucleus may 

 be seen in the unstained cells as a denser portion. 



