=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.