. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . ^-mm;^^ Fig 79.—Microscopic field, showing thetop of a hanging drop in a normal typhoidculture. Fig. 80.—Microscopic field, showing across-section of the drop in Fig. 79. In making the hanging drop to be examined it is necessary to haveit of such a depth that it will show at least three focal planes, other-wise the examination will be incomplete and unsatisfactory. Themoist chamber must be well sealed by vaselin so as to prevent drying,and kept at a temperature of at least 20° and not over 35°
. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . ^-mm;^^ Fig 79.—Microscopic field, showing thetop of a hanging drop in a normal typhoidculture. Fig. 80.—Microscopic field, showing across-section of the drop in Fig. 79. In making the hanging drop to be examined it is necessary to haveit of such a depth that it will show at least three focal planes, other-wise the examination will be incomplete and unsatisfactory. Themoist chamber must be well sealed by vaselin so as to prevent drying,and kept at a temperature of at least 20° and not over 35° Fig. 81.—Microscopic field, showing the topof a drop with the typhoid reaction. Fig. 82.—Microscopic field, showing across-section of the drop in Kg. 81. Fig. 79 shows a microscopic field of the top of a hanging drop ofa normal bouillon culture of typhoid bacilli. The culture is twenty 214 AGGLUTINATION AND PRECIPlfAtlON hours old and the organisms are freely motile. This represents theeotltrol drop used for comparison with the drop of the same culture towhich has been added a little of the blood of a person suspected to havetyphoid. Note these points in Fig. 79; the organisms are eveillydistributed throughout the field, except at the edge of the drop, wherethey are gathered in great numbers; they show great activity here,seemingly trying to crowd to the very edge. This attraction is prob-ably due to the action exerted on the organisns by the oxygen inthe air, which naturally exerts positive chemotaxis oti all aerobicorganisms. Fig. 80 shows a cross-section of the drop represented
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