CORRESPONDENCE                                    255

2. Life-history.—The phase of the life-history important from the standpoint
of infection has been already worked out by me. The eggs when they are passed
out with the faeces of the host have in them usually 16 or 32 segments of the
developing embryo. Eighteen to twentyfour hours after deposition, the embryos
are formed in the eggs. Eighteen to twentyfour hours after the formation of
embryos the larvae of the first stage are hatched out of the eggs. The larvae of the
first stage are active, but are not, capable of very great translocation.
After four days the larvae of the first stage become ensheathed and less active.
They continue in this ensheathed condition for about six days when the larvae of
the second stage emerge from them. These are again active, and after three to
four days of an active life the larvae of the second stage become ensheathed. The
ensheathed larvae are gradually transformed into the larvae of the third stage, the
infective larvae. The infective larvae do not come out of their sheaths outside the
host, but await an opportunity of being swallowed by the definitive host. The
development of the larvae in the cattle has not yet been worked out, since no
further opportunity has occurred for doing this at Muktesar, but this is not of great
importance from the standpoint of the transmission of the infection.

3. The mode of infection.—No doubt one of the modes of infection, as has been
suggested by the Live-stock and Dairy Expert, Assam, is through the food of the
cattle, the grass. The ensheathed larvae deposit themselves on the blades of grass
and when the latter are eaten by cattle, infection takes place. But this method of
infection is, in my opinion, probably of secondary importance. The larvae, as has
been said previously, not having been endowed with much power of translocation,
cannot voluntarily undertake a journey even to a distance of a few inches. The
only means by which the larvae can be distributed in the grass are by the actual
deposition of dung containing ova, the arrest of the larvae in the young grass
blades during inundations, and through the agency of the cattle themselves when
they walk along the ground breaking up the infected dung.

Another agency through which, in my opinion, the major portion of the
infection takes place is the drinking water. In a place like Assam which enjoys a
heavy rainfall the ground on which the infected faeces is deposited is often
inundated by rain water which accumulates in ponds and puddles and other larger
shallow collections. Most of the larvae, including those that are deposited on the
grass, would be carried along with the rain water and be stored up in such
reservoirs, which are the main stay of drinking water for most of the cattle
population in the province. In this way it is probable that the main source of
infection is the drinking water and not the food.

I deem it worth recording here that from an examination of all the worms
that were once recovered from a heavy infection of a dairy cow at Muktesar, from