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47
than the average have been increasing, and various factors have
been assigned as a cause of this increased virulence. The chief
causes are said to be, an increased virulence of the organism, and
a lowered communal immunity. The work originating in Leeds
suggests two strains of corynebacterium Klebs Loeffler. In 1931,
when investigating a severe outbreak of Diphtheria in Leeds, it was
ascertained that there were two kinds of Diphtheria bacilli, to which
the names of Diphtheria Bacillus Gravis and Diphtheria Bacillis
Mitis were given. The cultural characteristics of the two types are
said to be a definite and constant, though there are intermediate
types. As a result of .this work it was suggested (a) that the gravis
type is mainly, or even solely, associated with severe forms of
Diphtheria, (b) that the mitis type causes only mild attacks, and
(c) that attacks caused by the gravis strains respond less satisfactorily
to the ordinary anti-toxin prepared from the Park-Williams bacillus,
and that a special anti-toxin is called for.
Dr. O'Brien of the Wellcome Research Laboratories kindly
examined some swabs from the most severe of our cases. 10 swabs
were sent to him, and he reported that 6 were of the gravis type,
2 of the mitis type, and 2 contained bacilli of the gravis and mitis
types.
Exaltation of virulence has been denied by some
bacteriologists, and in an article in the British Medical Journal of
November, 19th, 1932, Dr. O'Brien and his co-workers set forth
the result of their experience. They stated that there is no satisfactory
evidence that the gravest types of Diphtheria are generally
associated solely or even mainly with the gravis types of bacillus.
If gravis and mitis cultures are injected into groups of guinea pigs
the two groups can be saved with' equal readiness by Park 8 antitoxin
given some hours later. Guinea pigs immunised with
prophylactic mixture which are impervious to human immunisation
in England and which are prepared from Park 8 strain survive the
injections of large doses of gravis cultures.
Bacteriologists, of course, can only determine virulence of
human parasites by the reaction upon adventitious hosts. It is
possible that Diphtheria may very in virulence towards man, its
natural host, and yet show no alteration in its behaviour to rabbits
or guinea pigs. There is room therefore for the clinicians
to express their opinion as to the character of the disease. It is
impossible for the clinicians to adduce evidence which is acceptable
to the pure scientist. It is always difficult to attain a reliable
history in a large number of cases. This is more particularly true
of the mild type of disease and of small children. But in some of
these cases, we were satisfied that the history was correct and that