I CHEMICAL MICROBIOLOGY RESEARCH UNIT, DEPARTMENT OF BIOCHEMISTRY, UNIVERSITY OF CAMBRIDGE, TENNIS COURT ROAD, CAMBRIDGE. TELEPHONE No.: CAMBRIDGE 56288 24 November 1956 Dear Dr Lederberg, Zany thanIts for the reprinjzs paper on protoplasts of E. coli. and the MS of your exchange reprints as you suT";est. I shall be happy to I was qreatly interested in the penicillin me tho since I have ion? thought that it has somethin!; to %do with cell wall me tabolism - a.%. see enclose3 reprint on effect of penicillin on electroghoretic mobility. It is indeed useful to have ,3fnethod for makincr coli protoplaats - I suppose they are strictly protoplasts, i.e. have lost their cell walk. I think it useful to define protoplasts in tstrms of cell m inus cell wall, don't you ? A definition in terms of a change to a spherical form which is osmotically sensitive seems to be inadequate and inconsistent with current botanic&& usaqe. I hope you will agree with this. I mention this because a number of papers are appearin in which the term 'protopLast4 is used in various senses. It m ight be useful to qet some joint statemaat on a definition as hapgene with inducible enzymes. I enclose what reprints remain and will senci future ones. Aours sincerely, -., - - I-" Kenneth XcGuillen Dr Joshua Lederberg, Department of ,Genetics, Univeristy of W isconsin, Madison, ~Aisconsin, u. s. A.