ABSTRACT
More than any other branch of science, biology came of age during the twentieth-century. In 1900, researchers in biology fell broadly into two categories: physiologists and medical researchers, who could claim to be practising real science with theory, experiment and observation; and 'naturalists', who were still doing little more than cataloguing facts and filling museums with specimens. Ever since the late nineteenth century, it has been known that infectious diseases can be caused by two different kinds of agent: bacteria, which can only be seen with a powerful microscope, and viruses, which are much smaller still. One of the more extraordinary capabilities of the human body is its 'immune system', the mechanism by which we recognise foreign organisms such as bacteria, or tissues transplanted from another organism. The human body can recognise mouse antibodies as foreign, and will attack them with antibodies of its own.
