1.   But the most pervasive and important mechanism is based on chemical substances called pheromones.

2.   Chemical Substances Pure substances have a fixed composition and well defined chemical and physical properties.

3.   Or again, take the multitudinous array of chemical substances that exist in the natural world.

4.   She took him to a place called the Loneliness Bar, where the hostesses wore swimsuits treated with a chemical substance.

5.   This symposium will address the question of effects of chemical substances on reproductive systems to both females and males.

6.   ...an oily liquid, basic to the manufacture of a host of other chemical substances.

7.   Psychoactive drugs are chemical substances that act on the brain to create psychological effects.

8.   Stoichiometry is the study of the quantitative composition of chemical substances and also the quantitative changes that take place during chemical reactions.

9.   All matter is composed of chemical substances.

10.   All chemical substances, whether elements, compounds or mixtures, are made up of three types of particles.