In this connection, however, the American results must be carefully borne in mind, and E. arvense must not too hastily be regarded as blameless.
Toxic Principle. It was for some years believed that the apparent toxic symptoms induced by Horsetails were due to Silica or to Aconitic acid—the latter a substance found by Matz and Ludwig. The conclusion come to by Weber, however, was that the poisoning by E. palustre is of an organic character, not due to silica. The young shoots, which contain little silica, were found in general to be much more poisonous than the old plants, which contain much silica. It was long since found by Wiggers that dried plants of E. palustre contained 8·88 per cent. of silica, but all species contain this substance in greater or less degree, and it varies considerably in amount, even in the same species. The feeding experiments conducted by Lohmann, with certain species of Equisetum, and the observed symptoms of illness after the consumption of some of them, particularly E. palustre, serve to show that the ill effects are neither to be attributed to greater or less digestibility, nor to the silica present. Neither are the aconitic acid and other organic substances, in part found in previous investigations, responsible for the poisoning. However, an active compound named Equisetine, a substance belonging to the alkaloid group, was isolated; this occurs usually, perhaps only, in E. palustre, at any rate in sufficient quantity to be dangerous to animals. Lohmann then, following up the investigations of Paucerzynski, Matz, Meyer, Weber and others, ascertained definitely that E. palustre contains an alkaloidal nerve poison, to which the name Equisetine was given, and the experiments were held to decide that this is the poisonous substance in this species. (As stated above, E. arvense was held to be harmless.)
Symptoms. At first, excitement and anxiety, followed by uncertainty of movement, reeling and staggering; paralysis of hind limbs at least, falling, possibly general paralysis, insensibility to external irritants, unconsciousness, and coma. Pulse accelerated, appetite at first normal, but in course of time great disturbance of nutrition; sugar in the urine. Course sometimes very acute, death occurring in a few hours, but sometimes protracted (two to eight days), and at times even chronic (one to several weeks).
In cattle, after excessive eating, continuous diarrhœa is characteristic, with paralysis; while, if the food be persisted with, cachexia and hydræmia combined with weakness bordering on paralysis make their appearance (Friedberger and Fröhner, via Pammel). In addition to cachexia, Pott also mentions colic, stoppage, bloody urination, abortion, and loss of teeth.
Young animals appear to succumb sooner than older ones, while grain-fed animals are more resistant than others. Referring to E. arvense Pammel says it produces paralysis of the rear extremities, and when death occurs spasms are noted. In relation to the poisoning of horses by the same species in hay Rich and Jones note unthriftiness, the animal appearing thin and the muscles wasted. In from two to five weeks, according to the age of the horse and the manner of feeding, the animal begins to lose control of the muscles, and there is swaying and staggering, though the eye is bright and the appetite good. If the plant is regularly ingested the horse loses the power of standing, becomes nervous, struggles to rise, the legs become more or less rigid, and at times all the muscles of the body seem convulsed. Even in this condition one well-nursed patient lived two weeks. The horses are generally willing to eat, although unable to rise, but become sore and tired from struggling, finally dying from exhaustion. Life is much prolonged by turning from side to side three or four times in twenty-four hours, thus preventing congestion. The pulse is slow till near the end, when it is rapid and weak; the temperature is below normal at first, but when the animal is down there is fever; the extremities are usually cold; and the lining membrane of the mouth, nose, and eye becomes pale.
Of Equisetum sp. Stebler and Schroeter say that they induce diarrhœa in cattle, which become poor, and in cows the milk yield is checked or ceases. Weber also refers to the effect on milk yield of E. palustre, which he says causes the milk of affected cows to become watery, poor in fat, and gives rise to a greasy, unappetising butter, while the yield may soon quite fail.
REFERENCES.
[2], [20], [57], [111], [176], [203], [204], [213], [220], [221], [222], [237], [260], [261].
FILICES.
Bracken (Pteris aquilina L.). The Bracken, Brake Fern, or “Fern” is of very considerable importance to farmers for four reasons: (1) It is a most pernicious weed; (2) it forms an excellent litter for stock and treads down into good manure; (3) it is said to have been successfully converted into silage; but (4) it has been accused of poisoning cattle.