108 Proceedings of Royal Society of Edinburgh. [sess. 
Fig. 3. — Deaths of Persons Aged 60 Years and Upwards. 
This curve shows the same seasonal variation as that of deaths 
from all causes, the maximum fatality being from November to 
January, and the minimum from July to September. The winter 
maximum is apparently associated with the prevalence of respira- 
tory complaints, from the attacks of which so many old people 
succumb. 
Fig. 4. — Measles. 
This, as regards the maximum, is rather an irregular curve, there 
being three well-defined periods showing a high death-rate, viz., 
the end of December, the middle of February, and the end of 
March. The climatic features of this extended period are a rather 
low temperature, small rainfall, but high humidity, although 
steadily diminishing. Towards the close of May the mortality 
greatly diminishes, the absolute minimum occurring in August. 
Fig. 5. — Wliooping-Cougli. 
This is essentially a complaint of spring and early summer, the 
mortality curve being above the mean from the second week of 
February to the beginning of July, and below it during the re- 
mainder of the year. This disease also exhibits three well-defined 
maxima, the first two of which coincide approximately with the 
corresponding maxima from measles. The primary maximum, 
however, occurs about five weeks after that of measles. Hence, 
whooping-cough is most fatal when pressure and temperature are 
high, and humidity at the annual minimum conditions intimately 
connected with the prevailing easterly winds. The disease is at a 
minimum in November. The climatic features of the months when 
the fatality from this disease is small are a low temperature, con- 
siderable rainfall, and great humidity, with an almost complete 
absence of winds from the east. 
Fig. 6. — Scarlet Fever. 
Scarlet fever is above the average from the middle of September 
to the end of February. It increases with great rapidity in October, 
reaching a maximum in the middle of November, when a rapid fall 
takes place, the disease in an epidemic form being virtually over 
