126 BOARD OF AGRICULTURE. 
For an adult the dose is four or five grains, twice a day, on 
every second day, for a week, the quantity to be diminished if 
the medicine causes ill effects, such as spasms, tenesmus, etc. 
It often causes temporary perversion of vision, things appear- 
ing of unnatural colors, etc., but this effect soon passes away. 
The root of male fern (see page 191), given in powder, in 
connection with purgative medicines, is also recommended. 
As means of prevention, the use of impure water should be 
avoided. And if water from streams and ponds must be 
used for drinking, as in most large cities, it should be 
thoroughly filtered through powdered charcoal. 
The Round-worm of the Horse (Ascaris megalocephala 
Cloquet). 
This species inhabits the intestine of the horse, ass, and 
mule, and is quite common. It closely resembles the preced- 
ing species in form and general appearance, but grows to a 
larger size, the male becoming ten inches long, and the female 
twelve inches or more. The mouth is surrounded by three 
large, rounded, very prominent lobes or papilla. In the male 
the tail is provided with wing-like folds along the sides; in 
the female it is conical, terminating in a point, the female 
genital opening being situated in the anterior fourth of the 
body. 
This species likewise produces vast numbers of eggs, which 
develop embryos externally to the body, in water. Dr. Cob- 
bold states that he has reared free, active embryos from these 
eges by keeping them five months in water. The horses, 
most probably, swallow these embryos in the water that they 
drink. 
These parasites, when numerous, will no doubt produce 
effects analogous to those caused in the human body by the 
preceding species, and the remedies will be similar. 
~The Round-worm of the Cat (Ascaris mystax Rudolphi). 
Although very common in the cat, this parasite is of inter- 
est chiefly on account of its occasional occurrence in the 
human intestine. 
It may be easily distinguished-by.the presence of peculiar | 
