In 1939 the insecticide DDT was added to the arsenal, and by the 1960 ’ s insect - borne disease was no longer regarded as a major threat to public health outside Africa.
છેવટે જીવજંતુઓનો અભ્યાસ કરવાનો રસ ધીમે ધીમે ઓછો થતો ગયો.