EQUISETACEÆ.
Horsetails (Equisetum sp.). A very great deal has been written on the subject of Equisetosis or Equisetum poisoning, and even at the present day opinion is divided as to which species are poisonous and to what extent. From the time of Linnæus there has been uncertainty as to the species, which has generally been given as E. arvense. Two German papers, by Weber and Lohmann respectively, published by the German Agricultural Society in 1903 and 1904, have done much to remove doubt on the matter, but cannot be said to have settled the question absolutely. These two papers seem to have been overlooked by some recent writers on the subject, but Lohmann’s appears to be the most authoritative paper yet written. Both are referred to below.
It seems to be definitely proved that certain species of Equisetum really are poisonous, hesitating statements notwithstanding. Chesnut and Wilcox state that there are cases of poisoning of both horses and sheep by E. arvense in the United States, though they are not common, and the opinion is expressed that “the plant, if deleterious, is evidently so only on account of its harsh scouring action in the mouth and intestinal tract.” On the other hand Rich and Jones record poisoning of horses by E. arvense in hay, but while adding that horses seem to develop a depraved appetite for the weed, they state that they have no evidence that horses grazing upon the green plant are poisoned. Güssow’s experience has been that cattle do not suffer any inconvenience at all from this species, or only very slight disturbance of the digestive organs, but that horses are conspicuously subject to fatal poisoning by it. Examination of hay on which a considerable number of poisoned horses were fed revealed in every case the presence of E. arvense. When the food was changed, horses, if not too seriously affected, made rapid recovery. (Treatment suggested is to change to easily digested food, give a sharp purgative, and follow by small doses of nux vomica three times a day.) Pammel says that in recent years a disease of horses in Vermont has been attributed to hay and fodder containing the weed; that it is proved by experiment that when ingested in sufficient quantity E. arvense is capable of causing fatal poisoning in horses, and is at times the cause of extensive losses; and that young horses are most susceptible, while grain-fed horses are less susceptible than others. He adds that sheep are supposed to be slightly affected, but cattle eat hay in which it occurs in large proportion with impunity.
Coming to the two German reports, it is stated by Weber (1903) that E. palustre contains a specific poison for cattle and other ruminants, but sheep and goats are able, owing to their fine muzzles, to separate it in fodder, and hence suffer less. Horses and pigs, he says, seem to suffer very little. Young animals and stock, from districts where the species does not occur, suffer more than those from places where it occurs—the latter appearing to learn early to avoid it.
Lohmann conducted feeding experiments with guinea-pigs with E. arvense, E. palustre, E. pratense, E. sylvaticum, E. maximum, and E. heleocharis (not British). He also fed E. arvense and E. palustre to horses, cattle, sheep, pigs, and geese in considerable quantities for many days on end; and made experiments with aconitic acid on guinea-pigs and horses. The feeding experiments with guinea-pigs showed that of the species named only E. palustre and to a less extent E. sylvaticum are poisonous plants (to guinea-pigs). With the large domestic animals the experiments showed E. arvense to be a harmless plant, and E. palustre to be really injurious to cattle but avoided by other stock. Lohmann considers that the many statements in the literature agree in part with this result, and that the divergent observations may be traced to various causes, among which perhaps an abnormal chemical composition of the weed fed plays a principal part.
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].