This table shows conclusively that the houses nearest the hospital were in the greatest danger of small-pox. It might naturally be supposed that the excessive incidence of the disease upon the houses nearest to the hospital was due to business traffic between the hospital and the dwellers in the neighborhood, and Mr. Power admits that he started on his investigation with this belief, but with the prosecution of his work he found such a theory untenable.
ADMISSIONS OF ACUTE SMALL-POX TO FULHAM HOSPITAL, AND INCIDENCE OF SMALL-POX UPON HOUSES IN SEVERAL DIVISIONS OF THE SPECIAL AREA DURING FIVE EPIDEMIC PERIODS.
+---------+---------------------+------------------------------------------------+
| | Incidence on every 100 houses within the |
| | special area and its divisions. |
Cases of |The epidemic periods +--------+---------+---------+---------+---------+
acute |since opening |On total|On small |On first |On second|On third |
small-pox.|of hospital. |special | circle, | ring, | ring, | ring, |
| | area. |0-¼ mile.|¼-½ mile.|½-¾ mile.|¾-1 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.
The greater part of these were attacked in the five days January 26-30, 1881, and in seeking for the source of infection of these cases, special attention was directed to the time about a fortnight previous viz., January 12-17, 1881. The comings and goings of all who had been directly connected with the hospital (ambulances, visitors, patients, staff, nurses, etc.) were especially inquired into, but with an almost negative result, and Mr. Power was reluctantly forced to the conclusion that small-pox poison had been disseminated through the air.
During the period when the infection did spread, the atmospheric conditions were such as would be likely to favor the dissemination of particulate matter. Mr. Power says: "Familiar illustration of that conveyance of particulate matter which I am here including in the term dissemination is seen, summer and winter, in the movements of particles forming mist and fog. The chief of these are, of course, water particles, but these carry gently about with them, in an unaltered form, other matters that have been suspended in the atmosphere, and these other matters, during the almost absolute stillness attending the formation of dew and hoar frost, sink earthward, and may often be recognized after their deposit.