AGf~ICULTURAL RESEARCH, PUSA.

38 PRACTICAL BACTERIOLOGY
there may be an inflammatory reaction at the site of the
injection. 'I'hese are regm'ded as due to a natural hypersensitiveness
to the horse serum. It is still doubtful whether
this condition is I'elatcd to anaphylaxis or to the so-called
" atopy" which is referred to latcr.
Hypersensitiveness to the products of the infecting
organism (allergy) is a feature of various infections
in man and animals, and can be demonstrated by the
general and local reaction manifested on injection of
preparations from cultures of the particular organism
-e.g. the tuberculin reaction (vide p. 303). In such
cases the sensitiveness can also be elicited by simple
cutaneous or intracutaneous tests. This form of
hypersensitiveness differs from anaphylaxis in certain
respects. Thus, it is doubtful whether such allergy is
dependent on a serum antibody, and it has not been
generally possible to transfer the sensitiveness to a
normal individual by injection of serum.
Atopy.-In certain persons as a result of genetic
factors, hypersensitiveness may occur towards a considerable
variety of substances of antigenic nature, so
that when the person is exposed to contact with the
substance to which he is sensitive, toxic effects result
-e.g. coryza, asthma, urticaria, gastro-intestinal
disturbance, etc. This form of sensitiveness has been
designated atopy, and is responsible for such conditions
as hay fever, asthma, etc. Substances to which
such sensitiveness can be attributed (atopens) are:
plant pollens (as in hay fever), dandruff of animals
(e.g. horse), proteins of various articles of food, etc.
Atopy can be tcsted for by cutaneous reactions with
preparations of the particular atopen, as in tcsting
bacterial allergy. While atopy cannot bc transferred
in the same way as anaphylaxis, it has been found that
when the scrllm of an atopic person is injected into the
skin of a nOll-sensitive person, and after an interval
the atopen is injected at the same site, an urticarial
wheal results. "rhe serum therefore contains somc
active substance (designated 1'cagin). This principle,
however, differs in certain rcspects from antibodies.