infection. The Wassermann test and the modern arsenical preparations
have not yet been in use for that period, therefore these figures, as an
estimate of the prevalence of syphilis in 1921, would not be materially
affected by these developments. An estimate based on these data may
therefore be regarded in the meantime as approximately correct.

During the past ten years 4,763 males and 3,747 females have been
admitted into New Zealand mental hospitals. The percentage of syphilitic
admissions of all types was 4.74, while the percentage of cases of
dementia paralytica was 3.89. In other words, of the admission of
syphilitics 82 out of every 100 cases were dementia paralytica. The
average yearly number of deaths from dementia paralytica according to
the Government Statistician's returns between 1908 and 1921 was just
under 40.

If Fournier's estimate that 3 per cent. of syphilitics ultimately
develop dementia paralytica be accepted, one would arrive at the annual
infection by multiplying 40 by 33, which gives 1,320. Assuming the
average duration of life, after infection, to be twenty-five years, this
means that at any given time there are twenty-five years' infections on
hand. Dr. Hay computed from this the number of persons in New Zealand
now who have, or have had, syphilis to be 1,320 x 25, equalling 33,000,
or 1 to every 38 of the population. If the average duration of life
after infection were assumed to be thirty years, the figures would be 1
to every 32 of the population.

Taking the figure for syphilitic infections over a period of years at
1,320 per annum, this would mean for the population of New Zealand
(exclusive of Maoris) 1 fresh infection annually in about every 850
persons.