Twort discovered discovered bacteriophages, a type of virus that attacks bacteria (the term bacteriophage was coined by Félix d’Herelle, who in 1917 independently confirmed Twort’s discovery). The discovery of bacteriophage began an immensely fruitful line of research that produced, among other things, Avery’s demonstration that DNA is the basic material responsible for genetic transformation (1944) and Alfred Hershey and Martha Chase’s “Waring Blender” experiment showing that DNA is the carrier of genetic information in virus reproduction (1952). For further information see the entry at HistoryofInformation.com at this link. Twort's paper is available at this link.