Before bacteriology, the cause of tetanus (lock-jaw) was unknown, and men were free to imagine that it was due to inflammation travelling up an injured nerve to the central nervous system. This false and mischievous theory was abolished by the experimental work of Sternberg (1880), Carle and Rattone (1884), and Nicolaier (1884), who proved, once and for all, that the disease is an infection by a specific flagellate organism. Their work was of the utmost difficulty, for many reasons. First, because tetanus, in some tropical countries, is so common that it may fairly be called endemic; and many of these tropical cases, there being no record of any external infection, had been taken as evidence that the disease can occur "of itself." Of this frequency of tetanus in tropical countries, Sir Patrick Manson, in his book on _Tropical Diseases_ (1898), says:-- "Tetanus is an exceedingly common disease in some tropical countries. In Western Africa, for example, a large proportion of wounds, no matter how trifling as wounds they may be, if they are fouled by earth or dirt, result in tetanus. The French in Senegambia have found this to their cost. A gentleman who had travelled much in Congoland told me that certain tribes poison their arrows by simply dipping the tips in a particular kind of mud. A wound from these arrows is nearly sure to cause tetanus. In many countries, so general and so extensive is the distribution of the tetanus-bacillus that trismus neonatorum (tetanus of newly-born infants) is a principal cause of the excessive infant mortality." Next, because the tetanus-bacillus has its natural abode in the superficial layers of the soil: here it is associated with a vast number of other organisms, so that its identification and isolation were a work of immeasurable complexity. What mixed company it keeps, is shown by Houston's estimate of the number of microbes per gramme in twenty-one samples of different soils. This number ranged from 8326 in virgin sand, and 475,282 in virgin peat, to 115,014,492 in the soil from the trench of a sewage-farm. In all rich and well-manured soil the tetanus-bacillus may possibly be present; but it was the work of years to dissociate it from the myriads of organisms outnumbering it. Next, because it cannot be got to grow in cultures exposed to the air: its proper place is below the surface of the soil, away from the air; it is "strictly anaërobic," and the attempts to cultivate it by ordinary methods failed again and again. It had to be cultivated below the surface of certain nutrient media, or in a special atmosphere of nitrogen or hydrogen.