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Scientific Memoirs by
quite possible that this may be the case ; but it appears a priori improbable, and
I should rather be inclined to attribute the absence of large tumours to their
having been re-absorbed, a process which would naturally take place with excep-
tional rapidity in so young an animal.
An examination of sundry specimens of grass, not known to be infected,
has led me to the suspicion that many of the free living nematodes which may
be found in such situations and which have hitherto been regarded as dis-
tinct species, may be but free-stage examples of certain parasites. In the
determination of this point, I believe that a comparison of the ova of mature
specimens will be of the greatest value, as in the two examples I have hither to
investigated the one point of resemblance between the free and parasitic
generations was the absolute anatomical identity of their ova. It need not,
of course, follow that because the normal method of infection is, by the ingestion
of embryos, indirectly descended from parasites, that the swallowing of direct
descendants would be unattended with risk. Indeed, the more I consider the mat-
ter the more I am led to the conclusion that it is a matter of absolute indifference
to the just hatched embryo whether it finds itself in free or in parasitic surroundings,
or whether it be the direct progeny of the parasitic or of the free stage. The ova
probably, however, cannot hatch out in the absence of oxygen as, for example,
would be the case if swallowed. The only difference would be that, by affording
these different surroundings, two brother emrbyos might be made to develop
respectively into the widely different free and parasitic mature adults. The
actual demonstration of this by experiment would be fraught with difficulties, and
could only be accomplished on an experimental farm. One would have, to begin
with, to raise some stock absolutely free from parasites, and widely distributed
as these now are, one would have to take lambs as soon they were dropped, and
to artificially feed them, throughout their life, with milk, and afterwards with
fodder which had been raised to a sufficient heat to destroy all parasitic life.
That this is no exaggeration is shown by the fact that I have never, in India,
thoroughly examined the carcase of any mammal without finding entozoa.
It is obvious that this power of being able to live and breed indifferently,
either as free nematodes or as parasites, adds immensely to the power of
the species to perpetuate itself.
Pathology. —Once one's attention has been directed to the matter, it is
impossible to mistake the appearances presented by this disease for any
other condition, except perhaps tubercular disease of the intestine, which is,
however, I believe, rare or unknown in sheep. The larger tumours form
coarse, naked-eye lesions, which can be seen and felt as hard opaque nodules,
even in the unopened intestine, hut can best be studied by slitting it open,
and, after thoroughly washing it, holding it up to the light, when even the
smallest tumours stand out as opaque dots. To make matters certain, stretch
a piece of intestine containing a medium-sized tumour over the tip of the
finger and snip out the tumour with a pair of scissors curved on the flat