344 INOEGANIO AGENTS 



and nerves become paralyzed by large doses. The convul- 

 sions occurring in poisoning are shown by experiments 

 to be due probably to stimulation of the hind-brain, 

 although they have been attributed to altered cerebral 

 circulation and to asphyxia. They are, however, pre- 

 sent during that period of poisoning when the blood 

 is of a bright arterial hue. 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 and its contained ganglia, 

 and also to irritation of the vagus centre. Moderate non- 

 toxic doses stimulate the vagus centre of the medulla, and 

 slow the pulse 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, or its ganglia, are directly influenced. Mode- 

 rate doses of prussic acid first stimulate, and then depress 

 the vasomotor centre. Arterial pressure is therefore prima- 

 xily raised considerably, but this is followed by a fall to, or 

 l)elow, the normal. 



Toxic doses stimulate the vasomotor centre very briefly, 

 a,nd this action is succeeded by profound depression and 

 paralysis of the centre, accompanied by a great diminution 

 of blood tension. 



Respiration. — Inhalation of the pure acid will cause 

 death in a confined atmosphere, and even inhalation of the 

 medicinal solution will induce the physiological symptoms 

 of the drug. The respiratory centre is usually depressed 

 from the beginning, by prussic acid, and the respiratory 



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