s~~~~~~~~~~~~~~~~~~~AN

twn its rePuttion as B6, i'ts old, name. Now its catalognumberlis BAS85. They're two numbers~for the same S&Snitrocelllose 0.451im mem1pranes. Either way, more re-searche~rs Use S&S~0.45m mebanes tan any otherbrand,, in circles for adsorptin of DNA strands and insheets to blot DNA fragments from gels. As the labora-tory standard, S&S is seiedan prfered 'in most othe ~papers publ'ished on RADAhbiization, pro-tein biniding assay-s, orRNA orDNA sequencing.

If you, dnt kniow wh,it's easy to find out. Fill inand mail the coupon to S&,and receive a free sample

ofS& A 85~-.-a 15c su re-rcircles up to 50mmdamter S lecmioarer Sc u l

Schleicher & Schuell, Keene, N.H. 03431 s-sPlease send me a free sample ofS&S BA 85 0.45/LLm membranes.El Circles . mm diameter or L-I a 15cm square.WMam..

IOrganization-I AddressICity/State/Zip-IMy application.

Schleicher & Schuell, Inc., Keene, New Hampshire 03431Schleicher & Schuell GnibH, D-3354, Dassel, West GermanySchleicher & Schuell AG, 8714, Feldbach ZH, Switzerland

Circle No.49 on Readers' Service Card

I Sato*, Z.. and R. W. Davis. 1977. Screening recombinant clones by hybridization1t@'1U%1j plaques in situ. Science. 196(4286):l180-182.

~.H,A.Lozeron and W. Szybalski. 1971. Techniques of RNA-DNA hybridizationtivalution for the study of viral transcription. In Methods in Virology. Academic

NNY. 5:271-292.

I M.,, J. Locker and S. B. Weiss. 1976. Tepyia apn fbceipaeIce~trarter tRNAs. J4 Biol. Chem. 251 (2) :536-547.

3enhardt, D. 1966. A memnbrane-filter telchnique for the detection of complementaryDMA. Biochem. Biophys. Res. Comm. 23(5):641-646.

ijjjespie, D. 1968. The formation and detecti.on of DNA-R-NA hybrids. In MethodsOf zymejogy. Academic Press, N.Y. Vol. Xli, Part B:641-668.

G,illespie, D. and S. Spiegleman. 1965. t\ quantitative aissav for DNA-~RNA hybrids withDMiw=bilized on a membrane. J. Mol. Biol . 12: 8'29-842 .

iumr, S. and W. Szvbanlski. 1969. Orientation of transcription oif the 1-a-c- operon andit. repressor gene in Esclherichia coli. 2. Melol. Iitl. '40:145-1531.

Loteron, H. A. and W. Szvbalski. 1,969. Cong'ruent tranacriptional controls anid heter-Aogy of base sequences in col iphages anid ,.'80. Virology. 39 37-388.

jozeron, 'H. A., W. Szvbalskt., A. Landlv,. . Abelson and J. 0.. Smith. 1969. Orienta-tioniof transcription for thie amber supressorrgencSO11 iq dOeternrined by hvbridiznat ionbetween tyrosine tRNA and thie separrated DNA str.an3 ofl tranIrsducing, uiphage .80dsu1 .J. A1. Biol. 39:239-24 3.

iygard, A. P. and B. D. Halt.I 1963. A mnethot-d for the (ictection of RNA-D)NA comnlexes.S1oches. Biophys. Res. Comm. l2(.1:98-10(4.

ligg, A., H. Suzuki and S. Bourgicoi.. 1970O. i-ric -:¾r initer-ict ion.- Mol. Biol. 48:67-83.

Schneider, Z. and A. Gluranowski. 1975. 1Detctrminaition o .2 nineby nI- ins o

aisorption on cellulose nitrate filters: -isns itive ii'1~ r m-i it ion oNf nuicl.eo-sidase activity. Anal. Biuchem. 6 : 491-111~4.

SIT, W., H. Echols and J. Adler. 19(1). COat rOl - v c -i A '.tcr lambda*hge infection and induction. Bie an11". -1,: ifS-1,I"--~-

4-Ytor, K., Z. Hradecna and W. Szybalskli. 1967- 1l.-;A,ne,mt-ril distri'ut ioi of the tran-

scribing regions on the complementary stran,ids oci ii ic )\.P Nat.Ai.57(6) :1618-1625.

Ri1. . C. and C. E8. Furlon-g. 1975).Prtfctoan ror i taorpamclutasate..aspartate binditng protc-inl from Eschlieifhi c>lj i P-I) Wtan 3092. J. Biol.

250(7):2574-2580.1

A plastic part exposed to certain liquids willcraze (develop small surface cracks). The same partin contact with other liquids remains unblemished.

The crazing occurs - often in seemingly inertfluids- only when the parts are under stress, eitherby design or from residual stresses locked in duringfabrication.

As a result, polymer scientists here at theGeneral Motors Research Laboratories havebeen investigating thisenvironmental stresscrazing phenomenon.In so doing, they de-veloped a method forpredicting whether ornot polycarbonate willcraze in the presenceof a wide variety ofliquids.

The investigationstarted with the mea-surement of the criti- UcaL or mimum, strain _at which polycarbonate crazes in numerous liquids.Attempts to relate these strains to established solubil-ity parameters proved unsatisfactory.

But after conducting experiments with additionalcRno IW OFpoaxcFpmoymn liquids, our researchers

cEucaseg ' discovered that forC3&wt.rtha1is liquids having equal sol-U 0.t1.0 ubility parameters, the

I _LowShWl0O measured critical strainincreased with molecu-

J lar size (liquid molarvolume).

This finding led }them to incorporate amolar volume factor

NonpolarMSou acty r (VO, on the map) intoV. (X8j86dr the solubility parameter

theory. The result: For the first time, a consistentordering of liquids according to critical strain.

So how do we now specify the maxumpolycarbonate strain level for a particular chemicalenvironment? The map tells us.

Polymer research: One way of trying to makeenvironmental stress crazing a thing of the past.

Howto squelch

an unpopular

craze

mn plastics..

General Motors

Research LaboratoresWarren, Michigan 48090

We currently have openings for Ph.D.s in engineeringor the physical, mathematical, or biomedical sciences. Ifinterested, please send your resume to: GMR Personnel,Dept. 915. An Equal Opportunity Employer.

SCIENCE, VOL. 201868

With some micro centrifuges,constant speed is a constant problem,but not with an Eppendorf.

Few other micro centrifuges designed for use with dispos-able test tubes spin as fast at constant speed as an Eppendorf.

Within ten seconds, the Eppendorf 5412 attains 15,000 rpm,generating a force of 1 2,800xG, regardless of load. Performancelike this means rapid sample separation, in most cases within60 seconds or less. An angled rotor accommodates twelve dis-posable Eppendorf 1 .5ml micro test tubes, or twelve 500,u1, 400,ulor 250,ul tubes using adapters. (For higher capacity requirements,the Eppendorf Model 5413 accepts forty 1 .5m!, 400,ul or 250,udisposable test tubes in four carriers, but operates at lowerspeeds.) Eppendorf Micro Centrifuges are equipped with auto-matic 15 min. timer, safety switch (prevents operation with lidopen) and safety lid lock (lid stays locked while rotor is spinning).

1.5m1 5OOAI 400AtI2 A

Eppendorf Micro Test Tubes have attached caps and areideal for centrifuging, mixing, or storing reagents. Economicallypriced, they are available in the following sizes: polypropylene1 .5ml, 500,u, 400,ul; polyethylene - 400,l, 250,ul.

For complete literature, write: Eppendorf Division, BrinkmannInstruments, Inc., Cantiague Road, Westbury, N.Y. 1 1590.In Canada: Brinkmann Instruments (Canada), Ltd.

ffMiciro CenrifugesCircle No. 3 on Readers' Service Card