REFERENCES.
[4], [16], [40], [50], [52], [73], [81], [141], [147], [203], [213], [257].
The Potato (Solanum tuberosum L.). Though potato haulm is more or less commonly utilised on the Continent as a green fodder, and has been so used in England, yet there are good grounds for the general belief that it is not a suitable food for stock. The tubers may in general be eaten with impunity, but, under certain conditions, cannot be regarded as blameless, since they have caused serious injury. There are certainly records of injury to man from eating Potatoes, and accidents with animals have occurred more commonly. “Greened” tubers, and tubers with young shoots appear to be the chief cause of accidents, and, as regards live stock, usually when fed raw.
Cornevin knew of no case of poisoning in man, and considered that this was probably because man (1) eats only the part poorest in the toxic principle (see below), (2) does not eat the skin, (3) always cooks the tubers, and (4) rarely subsists only on potatoes for a considerable time. He found accidents among animals, however, not rare. In fact, eliminating cases possibly due to changes caused by weather, cryptogams, and ferments, he found poisonings every year unquestionably due to Solanine, chiefly among cattle. Cows will eat the haulm without trouble in times of scarcity of green fodder, but to the detriment of their health if such feeding is prolonged.
Macfadyen showed some time since that old sprouted Potatoes, even after boiling, are poisonous to horses. In 1896 eleven horses died from eating in most instances small quantities of spoiled and somewhat sprouted Potatoes, and two test-horses fed on the Potatoes died. In this case, however, it was conjectured that the poison was probably some organic substance generated by the bacteria or fungi growing on the Potatoes.
Chesnut and Wilcox (1901) recorded the death of six pigs due to eating sprouted uncooked Potatoes; after cooking the potatoes did not cause poisoning. With sufficient boiling most of the poison appears to remain behind in the water and might be thrown away.
Cases of poisoning of stock by Potatoes appear to have occurred more or less frequently in Germany. Two such cases were noted in the Berliner Tierärztliche Wochenschrift in 1909, in one of which 64 cows developed symptoms of poisoning after being fed on a large quantity of raw tubers, while in the other instance two cows became ill after eating Potato parings—which, as shown below, contain more Solanine than the “flesh.”
In the case of two children who died, F. W. Stoddart, Public Analyst of Bristol, after a post-mortem in one case, gave a very guarded opinion that death was probably due to Solanine poisoning, due to eating raw Potato peel, but was not confident. A most interesting case of severe but not fatal poisoning is described in The Lancet (1899). No less than 56 soldiers in Berlin were badly affected, until the supply of Potatoes was stopped, but the men recovered.
Pammel (1911) states that some persons cannot eat Potatoes because poisonous to them, but such persons must be extremely rare, and hypersensitive to minimum quantities of Solanine, which is almost if not quite absent in the “flesh” of Potatoes.
Toxic Principle. The Potato plant, like the other species of Solanum mentioned above, contains Solanine, which occurs not only in the haulm, but in the flowers and fruits, and in the peel of the tubers. Solanidine also occurs ready-formed in the young sprouts of potatoes to the extent of 1·5 per cent. (Allen). In the case of the soldiers poisoned in Berlin analysis demonstrated the presence of Solanine to the extent of 0·038 per cent. in boiled tubers and 0·024 per cent. in raw tubers, and on an average every man who fell ill had 0·3 gramme of the alkaloid, a sufficient quantity to produce toxic results. Esser (1910) states that in midsummer the haulm contains 0·0925 per cent. of Solanine but late in summer only 0·0374 per cent. In the tubers the alkaloid occurs in the inner layers of the peel to the extent of 0·0124 per cent., red or pink varieties containing rather more than yellow sorts. The same authority says that damp soils tend to a higher percentage of Solanine than dry soils[[3]], and that nitrogenous manuring as compared with potash tends to an increase of Solanine. In fresh spring shoots 1·5 per cent. of the alkaloid has been found, and the percentage is especially high in tubers which have been “greened” by long exposure to light. As already stated it is the greened tubers which appear to be the chief cause of accidents. Tubers with young shoots are richer in poisonous alkaloids than those which have not yet been sprouted; such tubers when fed raw to stock may on occasion induce poisoning, unless fed only in small quantities.