Annotated: "The Virus Laboratory (University Hospital): Viruses are important disease producing organisms, smaller than bacteria, too small to be seen with a microscope. Unlike bacteria they grow only in living cells; many that affect man only in living human cells. In the flask on the left human cells are being prepared from human afterbirth. The technician in the centre, protected by the glass window, is putting virus onto such human cells. The technician (right) is examining such cultures for evidence of virus growth."