Essentials of bacteriology; being a concise and systematic introduction to the study of bacteria and allied microörganisms . n to a piece of ordinary note-paper. This isthen sent to the laboratory; the paper with the dried bloodis soaked for a few minutes in a watch-glass containing 4drops of clean water, thus obtaining a dilution of i : 5. Onedrop of this is then mixed with one drop of a bouillon cultureof typhoid bacilli of about twenty-four-hours growth, andexamined under the microscope in lie hanging drop. Weaker THE COLON-TYPHOID GROUP I4I dilutions of the serum have been recommended (i
Essentials of bacteriology; being a concise and systematic introduction to the study of bacteria and allied microörganisms . n to a piece of ordinary note-paper. This isthen sent to the laboratory; the paper with the dried bloodis soaked for a few minutes in a watch-glass containing 4drops of clean water, thus obtaining a dilution of i : 5. Onedrop of this is then mixed with one drop of a bouillon cultureof typhoid bacilli of about twenty-four-hours growth, andexamined under the microscope in lie hanging drop. Weaker THE COLON-TYPHOID GROUP I4I dilutions of the serum have been recommended (i : 50), andthis should be used in cases of doubt. So far, about 95 percent, of the cases examined, and which clinically were con-sidered typhoid fever, have given a positive reaction. It isnot often present until the fifth day of the fever, and dis-appears usually within a year, though in some individuals ithas been found ten years after an attack of the disease. The agglutinating properties have been found in nearly allthe secretions of the body—tears, urine, milk, pleuritic effu-sions serous fluid from blisters, Fig. 61.—^The Widai agglutination reaction (Slater and Spitta). There is no relation between the reaction and the bacteri-cidal power of the serum; the agglutination is not a destruc-tion. The agglutinating power is active, though the blood bedried and sealed up for months. It seems to have no directrelation with the question of immunity, since it occurs at theheight of the disease, and intense agglutinating serum maybe had in severe cases and in cases with relapses. A negativeresult does not exclude typhoid. The test is quantitative—i. e., it depends upon the dilutionof the blood-serum, since the serum of healthy persons instrong dilution will cause agglutination and loss of motility. 142 ESSENTIALS OF BACTERIOLOGY A serum in a dilution of i : loo causing complete clumpingin half an hour is undoubtedly typhoid. The culture must be kept in a vigorous condi
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