PRUSSIC ACID 359 



globin, and blood thus treated has no ozonizing property. Cyanohemo- 

 globin was thought to account for the action of prussic acid, but it does 

 not exist within the body in the blood of poisoned animals. The red 

 blood corpuscles are altered in shape by the action of prussic acid upon 

 blood withdrawn from the vessels. They generally become rounder, then 

 granular, and finally disintegrate and liquefy. But these changes do not 

 occur in the blood during life. The general action of prussic acid is 

 altogether independent of any influence upon the blood, since the same 

 toxic effect is produced upon the bloodless, or "salt frog" (vessels con- 

 taining normal salt solution), as upon the normal batrachian. 



Nervous system and Muscles. — -Prussic acid first stimulates the 

 hind-brain — as shown by convulsions, and excitation of the vagus, respi- 

 ratory and vasomotor centres — and then paralyzes the whole nervous 

 system. The brain, cord and nerves become paralyzed by large doses. 

 The toxicity of prussic acid on the nervous system has been shown by 

 Loeb to be due to interference with the oxidation processes in proto- 

 plasm. The convulsions occurring in poisoning are shown by experi- 

 ments to be due probably to stimulation of the hind-brain. The spinal 

 cord is paralyzed at a period after coma and convulsions have appeared. 

 The peripheral nerves and muscles are paralyzed directly by toxic doses, 

 and not through the mediation of the central nervous apparatus. This is 

 proved by shutting off the blood supply containing the drug, from a 

 frog's leg, and leaving the nervous connections intact, when no effect 

 of prussic acid is observed upon the limb. 



Heart and Blood Vessels. — Death sometimes occurs instantaneously 

 from large lethal doses of prussic acid, owing to diastolic arrest of the 

 heart. This action is due probably to paralysis of the heart (interfer- 

 ence with oxidation processes). Moderate non-toxic doses stimulate the 

 vagus centre of the medulla, without diminishing the force of the heart. 

 When the vagi are previously divided, this action does not occur, but 

 after large doses slowing of the heart is observed whether the vagi are 

 cut or not; thus showing that the heart muscle is directly influenced. 

 Moderate doses of prussic acid first stimulate, and then depress the 

 vasomotor centres. Arterial pressure is therefore primarily raised con- 

 siderably, but this is followed by a fall to, or below, the normal. 



Toxic doses stimulate the vasomotor centres very briefly, and this 

 action is succeeded by profound depression and paralysis of the centres, 

 accompanied by a great diminution of blood tension. 



Respiration. — Inhalation of the pure acid will cause death in a con- 

 fined atmosphere, and even inhalation of the medicinal solution will 

 induce the physiological symptoms of the drug. Therapeutic doses stim- 

 ulate the respiratory centre so that the breathing becomes quicker and 

 deeper. Toxic doses depress and paralyze the respiratory centre, its 

 ganglion cells being so altered by the poison as to be unable to utilize 

 oxygen. The breathing then is slow and deep. In the latter stage of 

 poisoning, the breathing is feeble and shallow, and only occurs at long 

 intervals. If death does not supervene immediately from diastolic ar- 

 rest of the heart, it comes on more slowly by asphyxia. The respiratory 



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