vi] Equisetaceae 85 



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 rumi- 

 nants, 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 



