|
Cases of|The epidemic periods +--------+---------+---------+---------+---------+
acute |since opening |On total|On small |On first |On second|On third |
small- |of hospital. |special | circle, | ring, | ring, | ring, |
pox. | | area. |0-1/4 mile.|1/4-1/2 mile.|1/2-3/4 mile.|3/4-1 mile.|
--------+---------------------+--------+---------+---------+---------+---------+
327 |March-December 1877 | 1.10 | 3.47 | 1.37 | 1.27 | 0.36 |
714 |January- | | | | | |
| September, 1878 | 1.80 | 4.62 | 2.55 | 1.84 | 0.67 |
679 |September 1878- | | | | | |
| October 1879 | 1.68 | 4.40 | 2.63 | 1.49 | 0.64 |
292 |October, 1879- | | | | | |
| December, 1880 | 0.58 | 1.85 | 1.06 | 0.30 | 0.28 |
515 |December 1880- | | | | | |
| April 1881 | 1.21 | 2.00 | 1.54 | 1.25 | 0.61 |
--------+---------------------+--------+---------+---------+---------+---------+
2,527 |Five periods | 6.37 | 16.34 | 9.15 | 6.15 | 2.56 |
--------+---------------------+--------+---------+---------+---------+---------+

Now, the source of infection in cases of small-pox is often more easy to
find than in cases of some other forms of infectious disease, and mainly
for two reasons:

1. That the onset of small-pox is usually sudden and striking, such as is
not likely to escape observation.

2. That the so-called incubative period is very definite and regular,
being just a fortnight from infection to eruption.

The old experiments of inoculation practiced on our forefathers have
taught us that from inoculation to the first appearance of the rash is
just twelve days. Given a case of small-pox, then one has only to go
carefully over the doings and movements of the patient on the days about
a fortnight preceding in order to succeed very often in finding the
source of infection.

In the fortnight ending February 5, 1881, forty-one houses were attacked
by small-pox in the special mile circle round the hospital, and in this
limited outbreak it was found, as previously, that the severity of
incidence bore an exact inverse proportion to the distance from the
hospital.