Bacterial endotoxins also known as pyrogens are lippopolysaccaride molecules attached to cell membaranes of gram negative bacteria.
Viruses are viewed as non living nucleic acids.
Detection of pyrogens is performed by injecting as sample into test rabbits, and monitoring their body funtions, such as temperature. In some instances they are measured with the more sensitive LAL (Limulus Amoebocyte Lysate) test. Pyrogens can cause fever when used on mammals, and can block cell and tissue growth in cultures.