Generally speaking the effects produced by the poisons of this group vary considerably. Among the arsenic compounds arseniuretted hydrogen, which is supremely a blood poison, must be excluded from the group and included among the blood poisons. ARSENIC, OXIDES OF ARSENIC Pure _metallic arsenic_ (As) is considered innocuous. _Oxides of arsenic_ especially are held to be industrial poisons such as arsenic trioxide (As₂O₃), the anhydride of arsenious acid (H₃AsO₃), a white powder, which is known under the name of white arsenic; _arsenic acid_ (H₃AsO₄), which forms crystals easily soluble in water, and the salts of these acids, especially copper arsenite, formerly employed in the production of dyes, and also _arsenic chloride_ (arsenic trichloride, AsCl₃). _Arseniuretted hydrogen_ will be treated separately as it has a completely different poisonous effect from that of the oxidic compounds of arsenic. _Arsenic sulphides_ (realgar, AsS₂, and orpiment, AsS₃) are regarded as innocuous in consequence of their insolubility in a pure state. But it may be remarked that arsenic sulphides (sulphur arsenic ores) which are used industrially, and even metallic arsenic, are to be considered poisonous, as they contain oxidic arsenic compounds in great quantity. Chronic arsenical poisoning is caused by gradual absorption through the respiratory or digestive tracts of small quantities of the oxidic arsenic compounds either in solution or as dust or fumes. The disease usually begins with digestive derangement which shows itself in more or less severe gastric and intestinal catarrh (loss of appetite, vomiting and diarrhœa); sometimes there are severe affections of the respiratory tract,—pharyngeal and bronchial catarrhs; often the illness is accompanied by skin affections of various kinds, rashes, pustular eczema, loosening of the nails, abscesses, dark pigmentation of particular parts of the skin, and other symptoms. The nervous symptoms vary much according to the severity of the disease; first of all, deafness and feeling of pins and needles, or loss of sensation (paræsthesia and anæsthesia) of the extremities. Further, rheumatic joint pains, weakness of the extremities and characteristic symptoms of paralysis occur, with accompanying atrophy of the muscles, and gradual loss of energy leading to total incapacity for work. Severe cases end in general exhaustion and loss of strength, with signs of severe injury to the central nervous system, such as epileptic fits, mental hebetude, &c. PHOSPHORUS _Phosphorus_ (P) is polymorphic; red (amorphous) phosphorus is innocuous, while white or yellow is poisonous. Phosphorus at various stages of oxidation is little if at all poisonous. White phosphorus is volatile and fumes in the air—the fumes consisting of phosphorus, phosphoric and phosphorous acids.