Now let us see how vaccination protects us from disease. We have mentioned above that the W.B.Cs. produce antibodies which neutralise the toxins produced by the invaders. These W.B.Cs. are of different kinds and each kind consists of millions of cells which recognise and combat a specific foreign invader. Once a class of W.B.Cs. has encountered a particular kind of invader, it develops memory and is thus trained to ward off future attacks. In this way the body becomes "immune" to that infection and the process is called immunisation. Thus, our body regularly develops natural immunity as a variety of fighting cells are produced by actual attacks of infectious agents. Artificial immunisation is a clever idea. It is done through "vaccination", that is by artificial introduction into the body of a weak infection, which triggers off a defence mechanism, and produces W.B.C. trained to combat that particular infection.