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.
On the other hand, Boehm and Knie, conclude that the main change is always exerted on the central nervous system - the medulla - the functions of which are for a brief period stimulated and then destroyed (Archiv fur Exper. Path. Klebs., Bd. ii., p. 137). In cats prepared for experiment according to their method, there occur under prussic acid at first two to four deep labored inspirations, then quick and convulsive expiration, "resembling that caused by irritation of the superior laryngeal nerve" (Rosenthal); they observe no inspiratory cramp or tetanus, and no influence of the vagi, whether it be left entire or divided, upon the course of the poisoning, nor upon the heart (v. p. 268). (The practical result is that these observers attach no value to atropia as an antidote, though equally with Preyer they recognize the excellent results to be obtained by artificial respiration.)
I am not prepared to reconcile the differences between these and other observations, but in a more recent essay Preyer attributes the differences to undue manipulation of the animals, maintains his conclusions unaltered, and offers additional facts in support of some of them (Archiv fur Exper. Path. Klebs., April, 1875). We must add, however, that Lecorche and Meuriot, while agreeing with him that cyanic death is connected with intense excitation of the vagus nerve, and that section of the vagi delays it, yet attribute such excitation to a central, not peripheral, action of the poison. A striking experiment made by Prof. Jones bears in the same direction: having found, with alligators, that the internal giving of the poison did not easily or quickly take effect, he applied it directly to the medulla oblongata, and within sixty seconds there followed complete expiration of the air contained in the lungs, with collapse of those organs, and tetanic contraction of the respiratory muscles (New York Medical Record, vol. ii.).
The convulsions which often occur in cyanic poisoning are cerebral in origin, for they do not occur in parts situated below a transverse section of the spinal cord - i.e., in parts with which cerebral communication has been interrupted (H. C. Wood). We may further conclude that they are connected with disturbed cerebral circulation, for they have been noticed to commence directly after cardiac arrest (Laschkewitsch, Coze).