VOL. 88, No. 2270

novement of the end of the bar (e) and assures aquick and positive movement of the valve when thevessel (d) moves from the "down" to the "up" posi-tion. A suitable counter weight is suspended fromthe bar (e).As indicated in the diagram, when the vessel (d) is

in the "up" position air pressure from the compressedair main forces the culture solution up into the sandcontainers. As the solution rises in the sand it alsorises in tube (b), the height of which is adjusted sothat when the solution has almost reached the surfaceof the sand it overflows and fills vessel (a) until thesiphon (c) is started. Vessel (a) then empties intovessel (d) where the weight of solution overcomes thebalance weight, causing the rotation of the valve (g),shutting off the compressed air and releasing the airpressure in the carboy. The culture solution from thesand containers drains back into the carboy, while theone-way glass valve in the tube (f) allows the culturesolution in the vessel (d) to drain back into the car-boy. By constricting this tube the frequency of irri-gation can be adjusted. When vessel (d) has emptiedit returns to the "up" position and in so doing againturns on the compressed air at the valve (g).

Other sand containers irrigated from the same car-boy are attached to the solution line (b) as indicatedat (i). When additional culture solutions are to beused their carboys need only be connected to the airline, as shown at (j). Carboys need not be of thesame size, but it is essential that the amount of solu-tion in each carboy be so adjusted that when thecompressed air is automatically shut off the level ofthe residual solution in all carboys is the same.

T. B. LOTTDOMINION LABORATORY OF PLANT

PATHOLOGY, SUMMERLAND, B. C.

A SIMPLIFIED TECHNIQUE FOR FORENSICPRECIPITATION TESTS

FORENSIC precipitation tests for the identificationof blood stains or other antigens can be carried outby merely placing small bits (1 sq. mm) of stainedfabric, very thin wood shavings or a few particles ofscrapings on a clean glass slide and adding one dropof the specific antiserum and control antisera to thetest objects. In the presence of the specific antiserum,a macroscopic precipitate appears almost as soon asthe object is thoroughly wetted. In normal rabbit sera.or heterologous immune sera no precipitate forms.The addition of a small cover slip to each spot flattensthe drop and makes it possible to observe the resultswith a hand lens or microscope. The cover slip isquickly sealed into position by drying of the serum atthe margin so that the slides can be examined in anyposition.The width of the zone of precipitation affords a

rough indication of the relative potency of the extractand the antiserum. A strong antiserum in the presenceof weak extract produces precipitate only around theobject, while a potent source of extract causes a muchwider zone of precipitate.The method has several advantages other than the

small amount of material required and the simplicityof the preparations. The preparation of extracts, andconcern for their strength and clarity, is unnecessary.The extraction occurs by diffusion and the extractsare clear and undiluted. The outward diffusion of theantigen creates the different proportions of extractand antiserum which favor maximal precipitation. Ithas been shown that extracts or antisera which are tooweak to give positive tests by the usual methods givepositive results under these conditions. Since noextracting fluids are required, such controls can beomitted.

Photographic records of the results can be preparedmore readily than in the case of tests prepared in tubes.Serological tests can be made under field conditionswhere only a lens, slides, cover slips and a few dropsof antiserum can be carried with ease.

JOHN H. HANKSSCHOOL OF MEDICINE,GEORGE WASHINGTON UNIVERSITY

BOOKS RECEIVEDAnnales de L'A.C.F.A.S.; Vol. 4, 1938. Pp. 359. 1

plate. Association Canadienne-Frangaise pour L -Avancement des Sciences, Montreal.

BURNS, ELMER E. Radio; A Study of First Principles.Third edition. Pp. xvi + 293. 236 figures. Van Nos-trand. $2.00.

CLARK, W. E. LEGRos and others. The Hypothalamius;Morphological, Functional, Clinical and Surgical As-pects. Pp. xii + 211. Illustrated. Oliver and Boyd,Edinburgh and London. 12/6.

GOODMAN, NATHAN G., Editor. Profile of Genius; PoorRichard Pamphlets: I, Life of Benjamin Franklin Yearby Year, 1706-1790, pp. 58; II, On Honesty, pp. 35;The Way to Wealth and Words of Wisdom, from PoorRichard's Almanack, pp. 35; On Peace, pp. 25; ThePractical Dr. Franklin, pp. 49; On Industry, Frugality,and Thrift, pp. 29; On Citizenship, pp. 39; On the Artof Virtue, pp. 34; On Religion, pp. 39. Franklini In-stitute, Philadelphia. Set, $2.25.

LEPESCHKIN, W. W. Wissenschaftliche Forschungs-berichte; Band 47, Kolloidchemie des Protoplasmas.Pp. xii + 248. 7 figures. Theodor SteinkopfE, Dresdenand Leipzig. 19 RM.

ORNSTEIN, MARTHA. The Role of Scientific Societies inthe Seventeenth Century. Pp. xviii+ 308. 14 plates.University of Chicago Press. $3.00.

SAYLES, LEONARD P. Manual for Comparative Anatomy.Pp. xi + 214. 55 figures. Macmillan. $1.60.

SCHOCH, EUGENE P. and WILLIAM A. FELSING. GeneralChemistry; An Introductory Course of Lessons andExercises in Chemistry. Pp. ix + 524. 73 figures.McGraw-Hill. $3.25.

WALTER, HERBERT E. Genetics; An Introduction to theStudy of Heredity. Fourth edition. Pp. xvii + 412.150 figures. Macmillan. $3.00.

WILLIAMS, SAMIJEL H. A Laboratory and Field Guideto Biology. Pp. xxv + 130. Macmillan. $1.25.

18 SCIENCE

12 SCIENCE-ADVERTISEMENTS VoL. 88, 'so. 2270

No. 10 Analytical Balance

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with suitable auxiliary apparatusof the intensity of

SOLAR RADIATIONA modified form of the Weather Bureau type described byKimball and Hobbs in the Journal of the Optical Society ofAmerica and Review of Scientific Instruments, Volume 7,No. 9, page 707 in an article entitled "A New Form ofThermoelectric Pyrheliometer," and also in the MonthlyWeather Review, Volume 51, No. 5, May 1923, page 239.

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Vol.. 88, No. 227012 SCIENCE-ADVERTISEMENTS

JILx 1, 1938 A3C1ENCEADVERTJSEMENTS 13

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JU-LY 1, 1938 SCIENCE-ADVERTISEMENTS 13

14 SCIEA CE ADVERTIKS!EMENTS VOL. 88, No. 2270

BINOCULARMICROSCOPE

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14 SCIENCE-ADVERTISEMENTS VOL. 88, No. 2270