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What is a germ? For thousands of years of his existence, man lived in ignorance of what caused disease. Primitive people had "explanations" and beliefs about the subject, the most common of which was that sickness was caused by evil spirits inside the body of the victim. It wasn't until 1865 that science was able to prove that germs were the cause of disease, and it was Louis Pasteur who first stated the germ theory of disease as we know it. Today we recognize that the most dangerous enemies of mankind are germs. These are tiny one-celled organisms, so small that we can't see them without a microscope, and in fact, some are so small that they cannot be seen at all! Germs, which are also called "microbes" and "micro-organisms," may be either plants or animals. The animal forms are called "Protozoa," and the plant forms are called "bacteria." A third group of germs is called "filterable viruses," which means they are so small that they pass through even the finest filters which hold back larger bodies. Every germ disease is caused by some particular kind of germ and by no other kind. For example, the germ of microbe that causes scarlet fever cannot cause malaria or any other sickness. Nor can scarlet fever be caused by anything except this specific germ! Many of the germs, however, which cause terrible diseases, have near-relatives which are not harmful but may be helpful to man. In most germ diseases, if the germs don't kill the patient, the body sooner or later destroys them and they disappear. In certain diseases, such as scarlet fever, measles, or mumps, one attack protects the patient from a second attack by the same germ. This protection against two attacks of the same germ is called "active immunity." Some animals possess a "natural immunity," which means they don't get diseases which attack other animals. Vaccination and antitoxins can give people immunity against attack by specific germs. Among the diseases caused by the smallest germs, the filterable virus, are: measles, rabies, chicken pox, infantile paralysis, the common cold, and influenza. Science still has a great deal to learn about these tiny, often-invisible organisms. Details
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