COUNTING BACTERIA IN TOMATO CATSUP 185 



slide is immersed in 95 per cent alcohol for one minute to fix 

 the smear, dried in the air, stained with Loeffler's methylene 

 blue for two minutes, washed off in water, dried and examined 

 with the iV inch oil immeision lens. The microscopic field is 

 then standardized by means of a stage micrometer, with the 

 selection of proper oculars and the adjusting of the draw tube so 

 as to bring the diameter of the whole microscopic field to 0.205 

 mm. Thirty fields are counted and the average for one field is 

 then multiplied by 3 on account of the dilution of the catsup, 

 and this result is then multiplied by 300,000. The result repre- 

 sents the number of bacteria per cubic centimeter of catsup or 

 other tomato product. 



Fifteen samples of tomato catsup or pulp were counted by 

 means of the Zeiss blood counter and by the modified direct 

 count, two counts being done on each sample, and the results 

 being averaged The able opposite gives the results in detail, 

 and a comparison can be made between the results obtained 

 from the Zeiss blood counter and by means of the direct count. 



CONCLUSION 



An examination of the above table will show that the direct 

 count gives much larger numbers of bacteria than the Zeiss 

 blood counter. 



Thus, the advantage of the direct count is, first, that a ba- 

 cillus can always be distinguished from micrococci or inert ma- 

 terial, while one is often in doubt when using the Zeiss counter. 

 Secondly, that micrococci can be counted since they are easily 

 stained and can be noted when this method is used. 



It is just as important to count the number of micrococci as 

 bacilli, since the former probably take just as active a part 

 in the deterioration of tomato products as the latter. Micro- 

 cocci are difficult to distinguish by means of the Zeiss counting 

 apparatus but are easily recognized when the direct method is 

 used. 



REFERENCES ' 



American Public Health Association 1915 Am. J. Pub. Health, 6, 1315. 

 Howard, B. J. 1911 Tomato Catsup Under the Microscope, Circular No. 68, 

 U. S. Department of Agriculture, Bureau of Chemistry, February 13. 

 Prescott, S. C, and Breed, R. S. 1911 Centralbl. f. Bakteriol. II, 30, 337. 



