Yet, on looking backward, I cannot help feeling that we, and especially I myself, were strangely blind to the obvious in the matter. I have already mentioned that when I rooted up a clump of grass in Regent’s Park it came away from the soil without resistance; and that when I examined the roots I found them almost as free of earthy deposit as if it had been grown in sand. That, coupled with what I already knew, should have put me on the track of the explanation; and yet I failed to draw the simplest deduction from what I observed. To account for this obtuseness, I can only suggest that already the idea of a “Blight” had taken root in my mind; and that I was so obsessed with the idea of a parasite that I never considered the facts from any other point of view. Since others proved to be equally slow in arriving at the truth, I can only conclude that they were misled in their mental processes much as I myself was. As I have said on a previous page, it was to Johnston, the bacteriologist, that we owe the discovery. It appears that he had been growing some bacteria in cultures; and, whether by accident or design, he had left one of his cultivation media open to the air. On examining the germs some days later, he had discovered in the culture a type of bacterium with which he was unfamiliar. He proceeded to isolate it in the usual way--I believe it is done by dabbing a needle-point into the culture and using the few micro-organisms which stick to the needle as the parents of a fresh colony--and he was amazed at its fecundity. There had never been such a case of bacterial fertility in his experience. A paper in the _Lancet_ brought the description of the creature to the notice of the scientific world. Johnston himself had not recognised the nature of the organism, as he had never dealt with this type of bacteria before; but from his description an agricultural bacteriologist named Vincent was able to identify it as being almost identical with one of the denitrifying group, from which it differed only in its immense power of multiplication. It was hurriedly christened _Bacterium diazotans_, on account of its denitrifying qualities. Further examination showed that its capacity for breaking down nitrogenous material far surpassed that of any known denitrifying agent. 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.