Symptoms resembling nitrobenzene poisoning in general are caused by _nitrophenols_ (C₆H₄.OH.NO₂), of which paranitrophenol is the most toxic; also by _dinitrophenols_ (C₆H₃[NO₂]₂OH), solid crystalline substances which melt at different temperatures, and the _mono-_ and _di-nitrochlorobenzenes_ (C₆H₄.Cl.NO₂ and C₆H₃.Cl[NO₂]₂). In cases of industrial poisoning by dinitrophenol, observed by Leymann, the workers were taken suddenly ill, with symptoms of collapse, pains in the chest, vomiting, distress of breathing, rapid pulse, and convulsions, and died within a few hours. At the autopsy a yellow substance was found with picric acid reaction which appeared to be di- or tri-nitrophenol. In other cases, some fatal, of industrial nitrochlorobenzene poisoning, also observed by Leymann, the typical grey-blue discoloration of the skin was obvious, and the chocolate-brown colour of the blood produced by methæmoglobin. _Trinitrophenol_ (picric acid, C₆H₂[NO₂]₃OH) is a yellow crystalline compound with bitter taste; poisoning by this substance exhibits clearly strong local irritant action (upon skin, mucous membrane, and intestinal canal, and especially upon the kidneys), besides effect on the blood and central nervous system. Prolonged action of picric acid upon the skin causes inflammation. Absorption of picric acid dust causes inflammation of the mucous membrane of the respiratory passages and symptoms of gastric and intestinal catarrh as well as inflammation of the kidneys. A jaundice-like discoloration of the skin and darkening of the urine are also characteristic; sometimes picric acid poisoning produces a rash resembling that of measles and scarlet fever. _Nitronaphthalene_ (C₁₀H₇[NO₂]) and _nitronaphthol_ (C₁₀H₆.NO₂.OH) in addition to methæmoglobin formation have an irritant action. It is stated also that dulness of the cornea is produced. _Azobenzenes_ also, which are to be considered as intermediate between nitrobenzene and aniline, form methæmoglobin (azobenzene, C₆H₅N = NH₅C₆).