The poisonous action of cyanogen and cyanogen compounds depends upon their power of preventing absorption of oxygen from the blood by the tissues with the result that the venous blood flowing to the heart retains the bright red colour which otherwise only arterial blood exhibits. This effect is due to cessation of the gaseous exchange in the body, and results in tissue suffocation. At the same time these poisons have at first an exciting and then a paralysing effect upon the central nervous system. In severe poisoning the nerve effect is masked by the effect upon the exchange of gases in the blood, since this quickly leads to death. Most of the cases of industrial poisoning under this heading result from inhalation; absorption of liquid cyanogen compounds through the skin can rarely come into consideration. If large quantities of hydrocyanic acid have been inhaled, death ensues very quickly. The person affected falls down suddenly, breathes with difficulty, the pulse soon becomes imperceptible, and after a more or less long stage of deep unconsciousness (coma) life becomes extinct. In slight cases of poisoning the patient feels a sensation of irritation in the throat, giddiness, sickness, and difficulty in breathing; occasionally such disturbances persist for some time. Some writers have described symptoms in workers manipulating prussic acid and cyanides, which they believe to be due to chronic prussic acid poisoning. Complaint is made of oppression of the chest, throat irritation, giddiness, difficulty in breathing, palpitation, hebetude, exhaustion, and nausea and vomiting; in certain instances the attack, aggravated by exhaustion and weakness, culminates in death. It is a question whether such poisonings are chronic in the true sense of the word. In view of the mode of action of hydrocyanic acid, such cases of sickness should rather be accounted acute or sub-acute poisonings through repeated action of small quantities of the poison. It may be mentioned that in persons working with alkaline cyanides (especially in electro-plating) skin affections occasionally occur; these are traceable to the caustic effect of alkaline cyanides. Treatment by oxygen inhalation with simultaneous artificial respiration holds out most prospect of success. This holds good for acute poisoning by the other poisons belonging to this group. Besides this, saline injections and bleeding are recommended, and also the administration of an infusion of sodium thiosulphate solution. _GROUP: ARSENIURETTED HYDROGEN AND CARBONIC OXIDE (BLOOD POISONS)_