138
This gives an average ratio of incidence of 1 case in 4,348 of the population.
This disparity of incidence on the sexes we are inclined to attribute to the facts as before mentioned, namely, that the female portion of the community are not subject to those conditions surroundings, food, ventilation, fatigue, etc.- which might probably be considered as predisposing causes.
It is worth notice that the prevalence for all practical purposes increases year by year among both sexes, in spite of the steady increase of population. Among the males the increase is four times greater in ten years, and among the females the increase is about the same.
The figures we have obtained, through the courtesy of Dr. I. MITCHELL, of admissions to the Alice Memorial and the Nethersole Hospital are so small as not to affect the general result as stated above.
We have to express our thanks to the Medical Officer of Health, Dr. PEARSE, for kindly supplying us with the estimated population.
Age Incidence.
The accompanying Table (No. IV.) shews the age at which patients were admitted. We may postulate that patients seek admission as soon as possible after the onset of the illness, as soon in point of fact as they are unable to earn a livelihood, and indeed the majority as soon as they feel the early symptoms of the disease.
Analysing the total number of cases in quinquennial age groups, it will be noticed that the disease did not occur in the very early years of life, viz., between 1-5 years of age. In the next period 6-10 years 7 cases were admitted, and 35 cases between 11 and 15 years of age. Then the curve rises suddenly and quick- ly, from the quinquenniad 16-20 to its highest, 21-25, and maintain their height during the next period 26-30. After this the curve rapidly declines as far as the period 41--45, and then there is a gentle fall in the next and following periods.
Taking the male and female admissions separately, it will be seen that among the males the curve rises rapidly during the period 16-20, and reaches and main- tains its maximum during the next two quinquenniads 21-25 and 26-30. There is then a notable fall to the next period 31-35, which continues during the next three periods. Thereafter the fall is gentle, steady and regular to the period 71-75.
The number of females admitted though small may be taken as fairly re- presentative of the incidence among them. We notice that the earlier age periods are those especially affected, there being a steady rise up to the period 16-20, after which there is a slow fall of the curve during the next two periods 21-25, and 26-30, then a rapid fall and the curve remains steady except one rise during the period 36-40.
Thus we see that the disease has its greatest incidence during the two quin- quennial periods 21-25 and 26-30, namely those years when the person is most vigorous and most fit for wage-earning. The extremes of life are affected to a very slight degree, but after the age of 30 although the curve drops fairly quickly we get large numbers, especially among the men, affected at the succeeding periods.
Seasonal Prevalence.
We have drawn up a chart to shew the admissions month by month during the ten years. Premising that the incubation period is from 20-30 days, and that the patients seek admission on the onset of the more severe symptoms which render them unfit for work, the chart is instructive.
We notice that the disease maintains a fairly uniform level during the first four months of the year. There is then a rapid rise in May and the level is main- tained during June. Then a further rise occurs rapidly in July and the curve maintains a high level in August and September. After that a sharp drop takes place in October, followed by a temporary rise in November, and a further sharp drop in December.