Infestation of the intestines with the commoner varieties of parasites is generally regarded as exercising no particular harm on the host, except to produce such general disturbances as digestive derangements or anemia, the latter being ascribed to the loss of blood through blood-sucking parasites and to the absorption of hemotoxic substances. Examples are not wanting, however, both among men, and among animals?notably the dog and the horse?of blood changes and many symptoms of disease which may be ascribed to the production by the parasites of toxic substances, capable of being absorbed and exercising harmful effects.