The Poisonous Principle of Lathyrus and Some Other Leguminous Seeds

Extract

Since remote times man has cultivated many kinds and varieties of peas and beans as food for himself and his domestic animals, and with two notable exceptions there has apparently been little suspicion on his part that they might be potentially poisonous or deleterious. The exceptions are the bitter vetch (Ervum ervilia L.) and the vetchling Lathyrus (L. sativus, L. cicera and L. clymenum), the former of which ever since Hippocrates recorded the first known epidemic and the latter since the seventeenth century have been recognised as liable to injure farm animals and to cause in man an incurable paralysis of the legs if eaten in too large quantity as part of the daily dietary. The bitter vetch is now only of limited agricultural importance as a cattle food, but lathyrus is extensively grown in France and southern Europe chiefly as fodder for farm stock and also to some extent for human consumption. The peasants cook and eat it like other pulses and the meal mixed with wheat or barley flour is made into bread, hence in times of scarcity and dear cereals an excessive use of it has often given rise to local outbreaks of poisoning. In India and in Kabylia the peas, whole or ground and cooked in various ways, form the staple diet of large sections of the poorer classes, as they are cheap, palatable, and very nutritious, and in times of famine the increased consumption has been the cause of many recorded pandemics. Apart from famines, however, large agricultural populations in some parts of India subsist to a great extent on lathyrus peas (khesari, teora, matra) and in certain States of North-West and Central India 6 per cent. of the total inhabitants are said to be affected in consequence by paralysis of the lower limbs, and in some of the worst villages 10 per cent. or more of the adult males. The condition has always been well known under various names to physicians practising in the countries affected, but in 1873 Cantani (Naples) gave it the name Lathyrism under which it is now usually described in text-books of medicine. As very large numbers of mankind habitually consume lathyrus peas it may safely be assumed that they are innocuous when taken as a moderate part of a mixed dietary, and Buchanan states that in some Indian jails 4–6 ounces per person have been given daily for years without any bad results having been observed, while on the other hand, Grandjean and others find that when they form almost the whole dietary paralysis supervenes in 4–8 weeks. But the grain varies considerably in its content of toxic substance and the results depend partly on this, partly on the amount eaten, and probably to some extent on individual susceptibility. Men are much more liable to be affected than women, in the ratio of 10 or 12 to 1, and boys than girls. Slight cases of lathyrism show merely a certain degree of motor paralysis and spasticity in the lower limbs which may pass off. In more severe cases the paralysis comes on suddenly and may involve the bladder, rectum, and genital organs, while there may also be pains round the waist, lightning pains, loss of sensation, numbness, cramps, and prickling. All these symptoms, if present, usually clear up with the exception of the spastic paralysis which varies greatly in degree and is permanent. Chevallier (France 1841) mentions somnolence as a symptom, Brunelli, who reported eleven cases which occurred in the neighbourhood of Rome (1880), states that after each meal certain of them showed a kind of transient intoxication, and Desparanches, who described an extensive outbreak round about Blois (1829), says that convulsive movements of the limbs is the earliest symptom in some cases. It is evident therefore that the poison may affect any part of the brain and spinal cord, but that its chief and permanent effect is exercised on the motor tracts from the cortex downwards. The general health remains good, and it does not directly shorten life. Lt.-Col. McCombie Young has published a very clear analysis and explanation of the motor clinical symptoms which makes any further account of them here unnecessary, and Proust's report on an outbreak in Kabylia also gives very full details. No post-mortem examination of the nervous system in man has ever been made.