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With these discoveries, the mystery of the new blight vanished. An examination of the soil of stricken areas showed that it swarmed with colonies of B. diazotans—to use the customary medical contraction—and the whole secret of the destruction was revealed.

It was evident that these new and super-active bacteria attacked the soil, disintegrated all the nitrogenous compounds within their range and thus left the plants without nourishment. The death of the plant followed as a natural result; but the matter did not end there. By destroying the nitrogenous compounds in the soil, the bacteria altered the whole texture of the earth in which they grew. All the nitrogenous organic matter which forms so large a part of the binding material of some soils was destroyed utterly; with the consequence that the mineral particles, which previously had been resting in an organic matrix, were now free to move. Only the clays retained their tenacious character: all other soils degenerated into sand.

There has, of course, been a great deal of speculation upon the origin of B. diazotans. Hartwell suggested that it came to us from Venus, propelled by light-pressure across the abysses of space. Inshelwood put forward the view that in B. diazotans we had an example of bacteria, originally endemic, changing their habits and spreading into fresh regions.