RESUMO
It is in the reinoculated cell line FL that the sensitivity of cells under the action of a small dose of diphtheria toxin (DT) changes to the toxin itself as well as to the Coxsackie enterovirus. (B-5). After surviving the infection and getting again "healthy", the cells have acquired simultaneously an elevated sensibility to DT and reduced susceptibility to B-5 transmissible even in long passages. These acquired properties are a transient phenomenon, after a certain number of passages the culture returns to initial stage with all properties inherent in the initial line of cells: with regard to DT in 10 months, to coxsackie virus in 7 months. The stage of elevated sensibility to DT and reduced susceptibility to B-5, however, may be not only renewed but also considerably prolonged and even strengthened by repeated contact of cells with a small dose of DT. The small dose of DT is the first delusion of the toxin not provoking any visible morphological changes in the monolayer. The experimental data obtained render it possible to presume that application of reinoculated cell cultures offers a promising method for studying manifestations of laws governing the third factor of immunity and allergy at the level of cells.