Vectors of infection

Dr Halliday Sutherland’s article, The Soil and the Seed in Tuberculosis, appeared in the British Medical Journal on 23rd November 1912. In it, he suggested that Consumption (tuberculosis in the lungs) was caused primarily by the spread of germs from an infectious consumptive to an uninfected person.

Eugenists disagreed. They said that Consumption was primarily an inherited condition. While they agreed that Consumption was caused by the bacillus tuberculosis, the condition was seen only in those whom had an inherited susceptibility to it.

Given that eugenists were often not medical doctors, how could they have known?

The answer was statistics.

It was Sir Francis Galton, the founder of modern eugenics, who realised that statistics could reveal whether features or conditions were passed on by heredity. It was his protégé, Karl Pearson (professor of the Galton Chair of Eugenics at London University) who applied these techniques to tuberculosis.

Here is a simplified explanation of how they did this: the diagram below shows a wife who is consumptive and a husband and two children who are not. If consumption is caused by infection, there is an equal likelihood that the husband and children will be infected. The data of many families were used to measure the frequency with which this was occurring.

If the disease was hereditary, on the other hand, a different pattern would be observed. The consumptive mother could pass her heredity to the children but not to her husband, who by definition did not share her genes.

Pearson’s statistical studies showed a higher correlation of Consumption in the children of a consumptive mother than in the husband of a consumptive wife. It was this, he argued, that proved that the disease was inherited, not infective.

Sutherland’s work at the St Marylebone Dispensary for the prevention of Consumption enabled him to study the disease and to prove that consumption was primarily infective and he published his findings in The Soil and the Seed in Tuberculosis. He explained that the reason that there was a higher incidence of Consumption in the child than in the father was because the immune system of the child was not as developed.

While Dr Sutherland was right, it was not until many years later that the conflicting views were resolved in favour of infection.

The picture shows a from “The Story of John M’Neil” Britain’s first cinema public health film, produced by Dr Halliday Sutherland.