This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
We are unable to conclude positively with Preyer that the peripheral ends of the vagus receive the first and main influence of the poison, for the mere extent of absorbing surface and ready contact with blood in the lungs would go far to account for the greater rapidity of the effects of inhalation, and there is other evidence that the respiratory centres are affected. This question, however, apart, we may accept the careful observations of Kolliker, that peripheral sensory nerves are paralyzed by local contact with sufficiently strong solutions, and the early disappearance of reflex function in cyanic poisoning is connected with such paralysis rather than with paralysis of the cord (Kied-rowski). Nerve-tissue placed in a solution of prussic acid loses its conducting power, and muscular tissue loses its irritability still more quickly, although the nerve-trunks are probably acted upon at the same time as the muscles after internal administration of the acid (Virchow's Archiv, Bd. x., p. 272). When the whole blood is rendered venous, as in later stages of poisoning, there is increased action of the contractile fibres of organic life (involuntary muscular tissue), and hence, often increased peristalsis of the intestine, contraction of the bladder, and evacuations from those viscera. The same result occurs sometimes in asphyxia from hanging, carbonic acid poisoning, etc., and is commonly attributed to the same cause (venosity of blood), though indeed it may result from paralysis of sphincters, as it does under chloroform, or during an epileptic attack.