ISTITUTO SIEROTERAPICO MILANESE “SERAFINO BELFANTI’” ENTE MORALE AGGREGATO ALLA UNIVERSITA DI MILANO Direttore Scientifico: Prof. Augusto De Barbieri Via Darwin, 2 - MILANO . . . “ti Direzione Scientifica TELEFONO n. 35.74.44 (5 linee) Jan. 24,1956 Dear Joshua,l am sorry for answring late your letter of Jan.2. I have been busy with various time-wasting occupations; 1 should now be relatively free from them, Book, I think the agreement was that you would write chapttrs 3,4 and & so that your present pian is quite satisfactory.I agree also about writing each chapter in fuli. The two chapters I sent you were prepared in a difterent way. The first one was in an aimost final form,except for data from papers I could not find,and which I hope you may be in a better position to read,in case they conta interesting informationmg on the early stages of sulpha drug resi- s$ance. The second one was a draft.As 1 adopted a somewhat new zka classification of drug actions etc, I was interestedito have your opinion about the pla af oitowed before setting down to write it in full. As you a€s now in a relatively free period ,it would be idea al if you could write chapters 3 and 4. This-wouid give me a more reasénable basis for writing chapter 5,for which I have prepared now much material,but imxmmk does to a larger extent than any other chapter depend on what has been said before regarding adap= tation of itdwidual cells and of higher organisms, Chapter 8 os to some extent independent of the rest.once I have your chapters 3 and 4 in hand i can go deep into writing the rest,and leave to you the final revision, The convention about referring to lines was the distance in cm. from the first line in each page. Hfr. It wili take me some time to trace ali the exrly history of the strain. However,tt was isolated some five or six times before it was lost in 1955,and stili now i find it useful to isolate it at intervals. Heaweuer, 1] have never tested recent reversions for F+ behaviour, Looking back at old protocols,i find that mtants esta- blished from the first Hfr,which were isolated obviously mmxz once or more after tne first initial isolation by which the strain was established (after selection for nitrogen mustard resistance) and were tested for Hfr behaviour after isolation,were later found to be F+. There is more than one occurrence of this phenomenon, thoug gh it is difficult to establish frequencies of reversions, I lost the strain about a year ago beaause liophiis died out, and in view of tts instability it was not kept on slants.Since I had it back from you I have practised two or three isolations, but ‘as 1 say 1 did not take interest in possible reversions. I would accept the idea that it is now more stable,but cannot say anyyhing aefinite about it. I have recentiy had some suspet that the closaess of the lin- kage between Hfr and Gal has decreased. G@ther facts iet me think that Hfr is likely to be some ambuiateny tactor,as you say . You ISTITUTO SIEROTERAPICO MILANESE “SERAFINO BELFANTI” ENTE MORALE AGGREGATO ALLA UNIVERSITA DI MILANO Direttore Scientifico: Prof. Augusto De Barbieri Via Darwin, 20 - MILANO Direzione Scientifica TELEFONO n. 35.74.44 (5 linee) f+ — Hf wili aiso have heard of Jacob and Woliman's ree¢ent findings ,clai-~ Ming that w+ x K+ crosses are ali due tormemlitr mutations. There is one major difficuity there ; why axg« is the progeny of F+ x Fe crosses F+ ? This was the datum that led Hayes to his vector theo- ry,out i do not sag how it cowid agree with therm present theory of the Pastorians, Their evidence comes from fluctuation tests,and replica plating,which permitted them to isolate several independa htr's,which showed difterent behaviours, Incidentaily,this is a case where the technique devéoped in our paper for streptomycin resistance and chioramphenicoi resistahce might be usetui to say how much ot their theory is courrect. Ynotpttuneteiy,tne disadavan- tage of Hfr in respect ot F# mist be fairly high in mixed cultu- res,thus making the experiment a dif'ticult one, the only interesting re:3ult,on which 4 am pianning to send shortiy a note to some journal, is that there 1s a sort of "mating reaction" in K-12; i.e. Hfr x Fe show fairiy strong agglutination in suitable mecnanical conditions,while He x He RMGWXAALSSRAELYOGREX or ifr x f+ show a tess sbrong: one,and this wouid be,it any, the Slmplest screeting test tor new tertile strains,It may,in some more or less distant furure,be come a diagnostic too. in bacteria ! 1 believe this is am magnitica'tion of the reaction that brings the celis ot opposite sex togeisher;some compiementarity of tne surfaces of celis of ditierent sex must ve the cause of 1it,as well as hating itseif. The observa$@ on was a byproduct,or statistical origin,of an entirely ditrerent experiment, Mixing Hfr and #- celis together i noticed a decrease in the number of viabie i- celis(incidentaisy, 4 understand iiaywes has made a simitar observa— tion: he thinks it due to xke a phenoimenon simiiar to lambda indu etion, due to some other phage or nfr itself), Trying to make gua counts for a kinetical *tudy, 1 found plate counts weee showed an abnormal scatter,which made the counts themselves unreliable, 1 therefore tested the hypothesis ,that the unreliabiiity or counts were due to clumping. The Lesson is : use the microscope more ote tan. Unfortunately,ciumping makes the counts iess reliabley and 1 Vind it ditricult to study the killing pnenomenon properily;but it 1s by itseit sutricieritiy interesting, perhaps,to deserve publLica=- tion of its own, I wisi answer Jsarry soon .I shouid certainly iixe to have _gone to Denver;it seeius a very attractive piace. I feei I shai stick to thigcountry » however, for a few more years,waiting for a better job. if none co mesf/ieanWiiie, i hope chances wixikxmak of finding good jobs in the States will not fade out. Yours . O-