P. aeruginosa has been found in many surface waters and soils and appears to be able to infect a number of plants. Pseudomonas can attack hosts ranging from man to insects and plants. Although Pseudomonas produces a number of toxic substances, their pathogenic significance remains unclear. The pulmonary host defenses against Pseudomonas have been analyzed by several groups. There are three major forms of Pseudomonas pulmonary infections: tracheobronchitis, pneumonia, and infection in patients who have cystic fibrosis. Pseudomonas infections of the eye have been known since the end of the 1800s. The most common form of eye infection is the corneal ulcer which can progress to panophthalmitis. Pseudomonas, like other Gram-negative bacteria, has been found in skin and soft tissue infections, abscesses of the liver and subphrenic areas, pericarditis, peritonitis, and vascular infections. Aerosol of polymyxin to prevent Gram-negative bacillary pneumonia has been tried with some success in reducing Pseudomonas pneumonia, but without reduction in mortality.