Lathyrism usually only supervenes when the use of the peas for food is prolonged, and the peas are taken in considerable quantity, but it is possible that there is wide variation in the toxicity of different samples, owing to differences in soil, climate, and other factors. In man, Lathyrism is stated to be common in Spain, Italy, Russia and India, owing to continued use of bread from flour of the three species of _Lathyrus_ mentioned above. It is said especially to affect males.
_Toxic Principle._ Nothing certain as to the poisonous properties is known, attempts to isolate the toxic substance having failed (Kobert), though Smith gives it as prussic acid, apparently indicating a cyanogenetic glucoside. This, however, can hardly be so, as the poison is cumulative, and may not show its effects for weeks or months, or, in man, even years—according to the quantity of peas eaten.
_Symptoms._ Lathyrism is only produced when the ration consists largely of the pea for a considerable period (see above); in the horse fed exclusively on the pea, the tenth day; but when one or two quarts are given daily, only towards about the 80th day. Moreover, the malady may declare itself as long as fifty days after the cessation of the pea feeding (Lander).
In general Lathyrism is marked by paralysis of the lower extremities in man and the hind limbs in animals, owing to the degeneration of the muscle fibres, and possibly to affection of the nerves. In _horses_ there is paralysis of the hind limbs, dyspnœa and roaring—with paralysis of the recurrent laryngeal nerve, and transverse myelitis. The horse thus shows weakness of the hind quarters, staggering in the effort to stand, difficulty in breathing, abnormally fast and irregular pulse, open mouth, distended nostrils. Tracheotomy often gives almost immediate relief.
Lander mentions in cart horses grinding of teeth, and convulsive movements of the eyes, recalling epilepsy. In one outbreak there was thick wind, staggering gait, weakness of hind quarters, and general signs of intoxication; and sudden violent attacks of laryngeal paralysis and dyspnœa during which there was palpitation, frothing, tongue protruded, eyes staring, bluish tint of buccal membranes, and palpitation. Paroxysms sometimes proved fatal.