THE DIRECT OR BREED METHOD FOR COUNTING 

 BACTERIA IN TOMATO CATSUP, PULP OR PASTE 



CHARLOTTE VINCENT 



Baltimore City Health Department, Baltimore, Maryland. 



Received for publication, August 8, 1917 



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 

 B. J. Howard (1911) in detail 



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 are 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 

 a sterile pipette calibrated to deliver 0.01 cc. the diluted catsup 

 is deposited on a second glass slide and evenly spread over an 

 area of 1 sq. cm. by means of a sterile needle. After drying, the 



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THE JOURNAL OP BACTERIOLOGY, VOL. Ill, NO. 2 



