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 mix 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 
