After absorption of the acids a decrease in the alkalinity of the blood can take place and in its power to take up carbonic acid, thus vitally affecting the interchange of gases in the body, and producing symptoms of tissue suffocation. As regards treatment in the case of acids and alkalis, neutralisation has been already mentioned; further, oxygen treatment may be recommended in cases where the blood has been injuriously affected. In cases of poisoning through breathing in acid vapours, inhalation of extremely rarefied vapour of ammonia or of a spray of soda solution (about 1 per cent.) is advisable. MINERAL ACIDS =Hydrochloric Acid= (HCl) is a colourless, pungently smelling gas which gives off strong white fumes. Experiments on animals, carefully carried out by Leymann, produced the following symptoms. Even in a concentration of 2-5 per thousand clouding of the cornea ensues, and after about an hour inflammation of the conjunctiva, violent running from every exposed mucous membrane with marked reddening, and frequently inflammation (necrosis) of the septum of the nose; the lungs are distended with blood, here and there hæmorrhages occur in the respiratory and also in the digestive tracts. The animal dies of œdema (swelling) of the lungs and hæmorrhage into the lungs if exposed long enough to the action of HCl, even though (according to Lehmann) there may not be accumulation of HCl in the blood; the chief effect is the irritant one; 1·5-5 per thousand parts HCl in the air suffices, after three or four hours’ exposure, to affect smaller animals (rabbits) so much that they die during the experiment or shortly after it. Man can tolerate an atmosphere containing 0·1 to 0·2 per thousand HCl; a somewhat greater proportion of HCl produces bronchial catarrh, cough, &c. The solution of hydrochloric acid in water is about 40 per cent. Simply wetting the skin with concentrated solution of hydrochloric acid does not generally have an irritant effect unless persisted in for some time; the action of the acid, when continued, has a marked effect upon the mucous membranes and upon the eyes. The same treatment already recommended in the introductory remarks on poisoning by inhalation of acid fumes in general applies. =Hydrofluoric Acid= (HFl), a pungently smelling, colourless gas, causes even in weak solutions (0·02 per cent.) irritant symptoms (catarrh of the mucous membrane of the respiratory organs, lachrymation, &c.). Stronger solutions set up obstinate ulcers, difficult to heal, in the mucous membrane and the skin. =Silico-fluoric Acid= (H₂SiFl₆) produces an analogous though somewhat less marked corrosive action. As regards treatment the reader is again referred to the introductory sentences on this group.