THE DIRECT OR BREED METHOD FOR COUNTING BACTERIA IN TOMATO CATSUP, PULP OR PASTE

Abstract

The method used for counting bacteria in tomato catsups , pulp or paste depends on the use of the Zeiss blood counter . In this method a drop of catsup diluted with two portions of distilled water is placed in the counting chamber so as to cover the space within the moat . This stands for fifteen minutes before counting . and the bacteria in 25 small squares are then counted and an average is obtained for 5 of these small squares . The result is then multiplied by 2 , 400 , 000 to find the number of bacteria per cubic centimeter . This method is described by In counting the number of bacteria per cubic centimeter in a number of samples of catsup I found that this method was not entirely satisfactory , as the bacilli are hard to differentiate from micrococci or various small particles found in the catsup . Mi- crococci a , re not counted according to this method as they are so liable to be confused with other bodies such as particles of clay . It was thought that these sources of error might be overcome by the use of the direct method of counting bacteria devised by Prescott and Breed ( 1911 ), and the same technique was used as that described under the " Microscopic Method of Analysis " in Standard Methods of Bacteriological Analysis of Milk . ( A . P . H . A ., 1916 ). The catsup is diluted with two parts of sterile water , since this dilution has proven satisfactory in counting most specimens when the Zeiss counting chamber is used . With I ....