ORGANIC POISONS AND DRUGS 97 



an unusually large feed would probably fail in this effect, 

 since the gradual evolution of the acid leaves time for 

 elimination and consequent diminution of the total effect. 



Absorption and Elimination. — ^Hydrocyanic acid and 

 its soluble salts are absorbed through the skin, speedily 

 producing the general symptoms. Similarly, the vapour is 

 rapidly absorbed through the lungs, and thus acts more 

 quickly than by the other channels of absorption. The 

 respiration, at first stimulated, is speedily inhibited. In 

 the circulation the venous blood, at first redder, is eventu- 

 ally darker. In a test tube hydrocyanic acid forms a com- 

 bination with hsBmoglobin, thus preventing the absorption 

 of oxygen. This effect appears to be absent in the living 

 animal, and it is likely that prussic acid destroys the 

 oxidising enzymes (oxydases) of the blood ; but it must 

 be remembered that hydrocyanic acid exercises a similar 

 retarding effect upon the activity of such inorganic ferments 

 as colloidal or finely divided platinum. When, for example, 

 hydrogen peroxide is being decomposed with evolution of 

 oxygen by means of finely divided or colloidal platinum, 

 the addition of a cyanide greatly checks the rapidity of the 

 change (Bredig). 



In addition, experiments upon the frog, which is very 

 resistant to ordinary asphyxiation, tend to show that the 

 poison also exercises a paralysing effect on the central 

 nervous system — rather more upon the medulla and lower 

 brain than upon the cerebral cortex. 



Elimination takes place through the lungs, the exhaled 

 air having a faint almond-like odour. In the blood it is 

 possible that ammonium formate is produced. 



Symptoms. — Very large doses are exceedingly rapidly 

 fatal, owing to the arrest of the heart in diastole. Toxic doses 

 usually exercise a brief powerfully stimulant effect, followed 

 by depression, paralysis, and diminution of blood tension. 

 Given by the alimentary tract, the diluted acid causes saliva- 

 tion, vomition if possible, and diarrhoea with the herbivorse. 

 There are convulsions, spasms, vertigo, paralysis, stupor, 

 and cessation of respiration before that of the heart-beats. 



7 



