The connection between certain conditions of
soil and the incidence of some infectious diseases
has long been recognised by Physicians but the way
in which these conditions operate has been variously explained.
This paper shows a correspondence between the
maximum of carbonic acid and the maximum reading of
the earth thermometer at three feet. Late summer,
when the temperature of the soil at three feet rose
to the maximum,showed also the greatest amount of carbonic acid. Throughout the entire year much rain
always produced a marked temporary increase in the
amount of carbonic acid. These facts probably find
their explanation in the increased bacterial life
called into renewed activity by the heat and moisture.
Moisture, as after much rain, may also act by
mechanically sealing up the pores of the soil and
thus preventing the normal escape of carbonic acid
into the general atmosphere. The highest reading of
the earth thermometer was towards the end of August
when it ranged in the neighbourhood of 56° Fahr.
Edinburgh is not what is known as a "Diarrhoea Town"
that is, one in which that disease plays havoc with
the infantile population in late summer and early
autumn, but still, it is observed that most cases of
infantile diarrhoea do occur at the time corresponding
with the maximum reading of the earth thermometer at
three feet, as is shown by reference to the Report of the Medical Officer of Health, Edinburgh 1898.
The diurnal variation in the amount of carbonic
acid showed an evening excess over the morning as
the year approached near to the summer solstice and
beyond it to the maximum reading of the year which
occurred in the last days of August. After this
period a morning excess over the evening was observed as the year approached near to the winter solstice and beyond it to the minimum reading of the
year which took place in the end of March. During
March, April and May, and again in September, October
and November, the morning and evening variations were
but little marked and temporary conditions of weather
probably produced them. The year may be divided as
regards the morning and evening variations in carbonic acid into four periods, September to December,
December to March, March to June and June to September. In the first and third of these periods the
morning reading is in excess,and in the second and
fourth the evening reading.
Any markedly high reading was always observed
to follow a high rainfall. Excessively low readings
on the other hand were observed after prolonged dry
weather. A temporary increase after rain was constantly observed.
The remarkable rise in the amount of carbonic
acid in February and March of 1895 during the period
of prolonged frost, and when snow lay on the ground
for about a month, is not easy of explanation. The idea suggested itself that perhaps this was due to
an increase of temperature in the soil caused by the
covering of snow preventing radiation of heat from
the upper layers of the soil. From observations
made in February 1900 I found that such a covering
of snow had no effect on the ground temperature thermometer whatever. The increase in carbonic acid may
be explained to some extent by the sealing up of the
surface of the soil thus preventing the natural
escape of carbonic acid into the atmosphere. It was
not observed that severe frost, apart from a covering
of snow on the ground, was followed by increase in
the amount of carbonic acid. In each of the three
years the highest reading was observed towards the
end of August.
The remarkably low reading in October 1896 and
again in August 1897 followed on a period of drought.
No observation was taken from February to June
Much rain was invariably followed by a marked
increase in the amount of carbonic acid.
No difference between the morning reading and
the evening reading of the earth temperature at three
feet was ever observed. The observations of the
ground thermometer readings were taken on three alternate days of each week. The annual range of the
temperature of the earth thermometer at three feet
was about 20° Fahr. The lowest reading was observed
to be in the month of February when it was in the
neighbourhood of 36° Fahr. and the highest reading in
the month of August when it was in the neighbourhood
of 56° Fahr.
There is observed to be a close correspondence
between the annual curve of the earth thermometer
and the annual curve of the amount of carbonic acid in the soil, that is, when the earth thermometer
reading falls to the lowest annual point or rises to
its highest annual point the amount of carbonic acid
in the soil similarly approaches its lowest and
It is further to be observed by reference to the
Reports of the Medical Officer of Health, Edinburgh,
that there was a close correspondence between
the greater number of fatal cases of Infantile
Diarrhoea and the highest reading of the earth thermometer at three feet.