Note 1 — Chapter III

The work of the English bacteriologist Twort, in 1915, and the Frenchman, d'Herelle, in 1917, brought to the attention of the scientific world the fact that many bacteria are subject to attack and destruction by some unknown active agent with which they are associated in infected material. This agent, whatever its character, changed growing germ cultures to a dead, glassy substance.

Twort advanced the thought that the agent might be a living, filtered virus, although he favored the theory that it was an enzyme derived from the bacteria themselves.

D'Herelle, on the contrary, believed that this phenomenon was due to a living, multiplying, ultra-microscopic microbe that destroyed certain bacteria.

Evidence favoring both theories has come to light, with the result that, at present, controversy is rife. Up to date, the contention of neither side has been proved.