GRALAB TIMER NEW -CATALOG

describes

15 MAettlertop-loading

b0balancesMettler's high-speed, easy-to-use, top-loading balances are

4510 fully described in a new cata-log. Included are units with performance levelsranging from semi-analytical to 11-kilo high ca-pacity. All are precise, rapid-reading and offer

40N1VER5A improved precision-to-capacity relationships.25 :Most unusual is the new Model P160. It features35 :a reversible scale for weight loss studies and gravi-

-30 metric titrations. Most versatile is the widely-usedP1200. Its 1200-gram capacity and -4-10-milligramreadability make it ideal for the vast majority ofroutine weighings.

All Mettler top-loaders can be used for five dif-ferent types of weighings. Included are weighingof unknowns, batching, check-weighing, weighing-

Easy to see and set! Large 8" dial can be set for any time in, and below-balance weighing.within range of 3600 distinct settings (1 sec. to 60 min., Request Bulletin P from Mettler Instrument Cor-

min. to 60 hrs., etc.). At end of preset interval, alarm poration, 20 Nassau Street, Princeton, N. J. 08540.sounds and external load is automatically switched on oroff. Split-second synchronous accuracy. Models at $26 to$36. Write for new 8-page illustrated catalog.DIMCO-GRAY COMPANY

207 E. Sixth St., Dayton, Ohio 45402Circle No. 78 on Readers' Service Card Circle No. 72 on Readers' Service Card

Circle No. 47 on Readers' Service Card

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20 SEPTEMBER 1968 1263

New0$26 IJnwversityKit

demonstratesGel Filtration.

Now, for the first time, all the materials necessaryfor teaching and demonstrating the gel filtrationtechnique to chemistry students are together in aconvenient, economical self-contained unit...theSephadex® University Kit. Here's what you'll findwhen you open the handy carrying case:

1. A standard Sephadexe Laboratory Column,K9/30.

2. Sephadex- one vial each of G-25 and G-100.3. Six sample vials- each containing a mixture of

three different molecular weight colored mate-rials.

4. Instruction manual containing a full 45-minutelecture outline and suggested experiments.

This complete teaching aid is indispensable foruniversities, research institutions, and industriallaboratories interested in acquainting students andresearchers with the Sephadex gel filtration tech-nique so widely used in research and industry for

b the fractionation of biological materials.W To order your Sephadex University Kit, complete the couponr below and return it to us.

PHARMACIA FINE CHEMICALS INC.* .i- 800 Centennial Avenue, Piscataway, New Jersey 08834ILL/I Pharmacia (Canada) Ltd., 110 Place Cremazie,

n Suite 412, Montreal 11, P. Q.(lnquinies outside U.S.A. and Canada should be directed toPHARMACIA FINE CHEMICALS AB, Uppsala, Sweden.)

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Name Title_(Please Print or Type)

Organization

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Field of UseCircle No. 22 on Readers' Service Card

A. M. Burt (Nashville). Plant tissuewas found more difficult to prepare thananimal tissue. The prevention of virusredistribution in plant cells during thepreparation for autoradiography wasdiscussed by D. E. Schlegel (Berkeley)and W. G. Langenberg (Lincoln). Thesuperiority of section freeze-substitutionin the preservation of certain enzymereactions compared to classical fixationand embedding techniques was demon-strated by J. P. Chang (Houston). Al-though this method has been used forthe tissue preparation in autoradiog-raphy, the application of an organicsolvent, albeit at low tempercature,may obviate its applicability in theautoradiography of diffusible com-pounds. The implications of freezingand thawing for maintaining tissuestructure and viability were discussedin two papers by H. T. Meryman(Bethesda) and B. F. Trump (Durham).It was emphasized that ice crystal dis-ruption and cryosmosis probably can-not be eliminated but may be mini-mized by rapid freezing and mainte-nance of low or ultralow temperaturesduring tissue preparation. Preliminarydata on the utilization of low-tempera-ture tissue cutting for electron-micro-scopic autoradiography were shown byT. C. Appleton (London) with a cry-ostat microtome and by A. K. Christen-sen (Stanford) with a freezing micro-tome. The subcellular morphology inthe presented photomicrograms ap-peared different from those obtainedby classical fixation and embeddingprocedures. Considerable improvementof technique will be needed, however,before judgments on authenticity canbe made and classical pictures are chal-lenged. Electron-microscope autoradi-ography of diffusible compounds willhave to await the perfection of low-temperature tissue preparation and, asS. Ullberg (Stockholm) pointed out.the present situation is such that itis still not realizable but promising, ashe stated 4 years ago at the confer-ence on Isotopes in Pharmacology heldat the University of Chicago, Centerfor Continuing Education, June 1964.That such hope is justified was elo-quently demonstrated by M. M. Sal-peter (Ithaca) who provided modelsfor a quantitative approach to the eval-uation of resolution and sensitivitybased on progress made in EMAR withclassical preparative techniques.

WALTER E. STUMPFDepar0tn)enit of Plhatitnacology,University of Chicago, 947 East 58Street, Clhicago Illiniois 60637

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