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now as, owing to the small number of the horses, a good method could not be aban-
doned for a possibly better one- as long as the efficacy of the serum was not univer-
sally acknowledged.
After all that has been said about the errors of statistics, it is hardly necessary to
repeat that the number of observations must be large. If I should be called upon to
fix this number, I should say that at least 500 comparable observations will be
necessary in order to allow reliable statistical conclusions, But if the observa-
tions are made under the varying conditions of different surroundings or by persons,
not familiar with the treatment, new unknown factors are introduced and the number
of observations has to be still further increased. It is for this reason that the experi-
menters are as yet reluctant to have the observations scattered over different places,
the supply of serum being still limited.
The issue at stake is of such great importance that every step forward has to be
taken with the utmost precautions in order to avoid accidental non-successes. These
remarks may also be applied to the use of the serum in private practice where the
indiscriminate administration of the serum may discredit it in single instances.
This disadvantage, however, will be greatly counterbalanced by the favourable condi-
tions of application, and we may expect from private practitioners early accounts of
good results.
What are the best results we may hope for in hospitals ?
Provided future epidemics are not of increased virulence, the percentage of re-
coveries ought to be higher than it was in the selected cases. Firstly, because the
results of the past have been obtained in patients who, owing to the selection, would
have had an increased mortality under the ordinary treatment, and secondly, because
we may expect that sooner or later the production of a serum of the highest activity
will be the rule.
The efficacy of a serum must not be judged by the average results which have
been obtained, but by the best results. If a serum with high curative properties has
once been prepared, it will be possible to prepare it again, and with certainty. This
is merely a question of time and experience.
Considered numerically, it may be said that about 30 per cent. of the patients at
the large plague hospitals die within the first 24 hours after admission, and that re-
covery in them will be exceptional even with the best serum. Within the next 24 hours
another 20 per cent. die : that many of these may be saved is open to doubt.
About 20 per cent. recover under the ordinary treatment. Thus there remain 30
per cent. in which there is the possibility and probability of the serum influencing
recovery.
An increase of the recovery rate from 20 per cent. to 50 per cent. is what, we
can confidently hope for.
It can be said that this does not correspond to 26 recoveries in 30 cases treated
by Prof. Lustig in 1897. To this I would reply, that a generalisation from the lower
to the higher number is in itself erroneous, that the average recovery rate in 1897
was 15 per cent. to 20 per cent higher than it is now, and that the treated patients
were mostly Mahomedans or soldiers of good physique, well fed and brought early
to the hospital—all the above conditions being favourable to the serum treatment.
That by the serum treatment a mortality of 80 per cent. should be reduced to an
insignificant number, as some demanded, is an exaggeration which could only have
been indulged in by those who were ignorant of the clinical features of plague.