10 
INTRODUCTION 
works. Thus the English or house sparrow is called Passer 
domesticus, and the American elm, Ulmus americana, so that 
scientists of different countries may always use the same 
term. But in this book we shall use the common -Ameri¬ 
can names of the plants and animals studied. 
Scientific terms include also names frequently referred to 
in science books like this Biology, such as physical and 
chemical change, environment, and energy. 
Physical and Chemical Change. — If a solid piece of ice 
is melted, it becomes liquid water. If the liquid water is 
boiled, it becomes gas (steam or vapor). If the steam is 
condensed, it becomes water, which in turn may again be 
frozen into ice. Any change in a substance which does 
not alter the material of which it is composed is called a 
physical change. 
On the other hand, when oxygen unites with wood, the 
wood may burn, giving off heat and smoke, and ash remains. 
But this ash cannot be united with heat and smoke to form 
the original wood. Such a change as is seen in the burn¬ 
ing of wood is called a chemical change. 
Organic and Inorganic Matter. — It is customary to 
separate chemical compounds which are made in living 
things from those which are made outside the bodies of 
plants and animals. All matter such as wood, sugar, and 
meat, which is made in living things, is called organic matter. 
All matter, like stones and water, which is made outside of 
living things, is called inorganic. 
Environment. — Plants and animals have accustomed 
themselves to live in different parts of the world. Their 
behavior and habits under these varying conditions form 
a most interesting part of the study of biology. The sur¬ 
roundings of plants and animals, that is, the different con¬ 
ditions, the air, water, climate, and soil in which they live, 
are called their environment. 
Energy. — To carry on the fundamental processes of 
