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THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY. [V, III
and biochemistry of organisms usually not more than half a millimetre long. The
writer's unpublished work on these larvae shows, nevertheless, that such work
might give us valuable information.
A great deal of work has been done by various workers upon the so-called
excretory products of adult nematodes. It is as inconclusive as the work, which
is bound up with it, on the question whether nematodes are aerobic or not. Slater
(1928) has investigated this latter question and summarises much of the work
upon it. The balance of evidence is, perhaps, in favour of either anaerobiosis or
some special mode of respiration, which may be akin to that of muscle. The
absence from nematodes of specialised respiratory organs also favours this view,
as do also such facts as the very low oxygen consumption by the non-parasitic
larvae, and the toxic effects of high oxygen tensions upon them (McCoy, 1930).
The appearance of fatty acids in media in which nematodes are kept seems also
characteristic of them, but it is not yet clear whether these are specific products
of nematode metabolism, or of some association they establish with bacteria. If
we knew the truth about these questions and could more precisely determine
the respiratory and excretory processes of nematodes, we might be able either
to deprive them of substances vital to their life, or prevent their excretion of sub-
stances which could be toxic to them if they retained them in their tissues. We
should also be in a better position to distinguish between the mechanical damage
they cause to their hosts and that due to specific effects of their metabolism upon
the host's physiology.
Enough has perhaps now been said about some aspects of the physiology
of parasitic nematodes to emphasise the gaps in this important field of knowledge
and to support the view, expressed by the writer elsewhere (1933), that little
advance in our control of these parasites is to be expected, until we can relate
their physiology to that of their hosts and determine their relationship to the
other organisms which may form part of the complex of commensals and parasites
living inside their hosts. It is a state of equilibrium between all the members of
this complex that we should seek to maintain, because that is the solution of our
problem which nature herself adopts. Our task, in other words, should not be the
impossible one of attempting to rid human beings or farm animals of all their
nematode parasites, or of trying to keep them free from these, but the very
difficult but at least possible one of keeping these infections within bounds. It
has already been pointed out that, so far as domesticated animals are concerned,
the examination of any marketable animal in a slaughter house will show that it
has harboured many nematodes without serious damage to its health ; and it is
always possible that worm-free animals, even if they could be produced at an
economic profit—which at present they certainly could not—would not be as
healthy as individuals developing freely in nature, or on a farm, and therefore
containing parasites, for the reason that the latter have evolved in association with
these parasites and therefore are adapted to their presence. If we could produce