This book has been developed as part of a course that will prepare you for a career in the health or natural sciences. The information it contains is highly technical and it provides a foundation for the practical hands-on work and critical thinking that are an integral part of many science based professions. You will need to understand concepts such as cell structure physiology disinfection drug actions genetics pathogenesis transmission of diseases and immunology just to name a few. Like all science courses this type of course will require prior preparation background and significant time for study. You will need to develop a working knowledge of terminology and definitions and to learn explanations of the "how and why of many phenomena. Like all learning, it can be a lifelong discovery experience that makes you a well-informed person who can differentiate fact from fiction and make well-reasoned interpretations and decisions.