[The presence of a hypothetical extracellular fraction in integral typhoid vaccines prepared on a semi-synthetic medium (author's transl)]. 
The Authors have carried out a research on the purpose of explain the action of a typhoid vaccines prepared on a semi-synthetic medium, which in preliminary tests on mice and men evinced good immunizing power.  The tests now performed demonstrate that an acellular filtrate of the vaccine (obtained from 24 h old culture) showed have the characteristics of an exotoxin and developes a strong immunizing power.