A lysozyme is a part of the innate immune system. They are enzymes which are in mucus secretions like saliva. They protect against infection by chopping up the bacteria, viruses and fungi which infect animals.
The name 'lysozyme' was coined in 1922 by Alexander Fleming (1881–1955), the discoverer of penicillin. Fleming first observed the antibacterial action of lysozyme when he treated bacterial cultures with nasal mucus from a patient suffering from a common cold.