356 THE HUMAN MACHINE 



using the food taken into the body to do this. We also 

 know the auto cannot repair itself if injured, while our 

 bodies if cut or bruised will soon heal if we are in good 

 condition. And perhaps most important of all, while 

 the auto has to be directed from the outside, the human 

 machine is self-directed. And each human machine is 

 an individual, alike in general pattern to every other, yet 

 different. Anyone of us may accomplish great things 

 if we have our machine in perfect condition, or we may 

 be handicapped throughout life by not knowing how to 

 get the most out of it. 



The Building Materials of the Human Machine. We 

 have already learned that plants and animals are made up 

 of living units of living stuff called cells. The human 

 machine is also built of these tiny bits of living matter. 

 They are so tiny that it would take several thousand to 

 fill the space made by this letter O. 



Demonstration 1. Body Cells. 



Scrape the inner surface of the mouth with a clean spoon. 

 Wash off the scraping, on a glass slide, with a drop of water, add a 

 drop of blue ink and examine under a compound microscope. The 

 structures seen are cells which make up the inner lining of the mouth. 



Every cell has a body made of living matter, while 

 within it is found a darker staining structure called the 

 nucleus. We shall find in our later study of biology that 

 the nucleus has a very important work in the division of 

 cells. As the body grows, the cells of which it is composed 

 are constantly dividing to form more cells, so that our 

 bodies are formed by the multiplication of cells. These 

 cells do not grow in size, but in number, and it often hap- 

 pens that a very large animal or plant is made up of small 

 cells, while a tiny one may be made up of very large cells. 



Demonstration 2. Cells in Hay Infusion. 



Place a drop of a hay infusion under the low power and see how 

 many different kinds of cells you can find. 



