EXAMINATION OF FLUIDS AND SOLIDS l8l 



readily grasped by the mind and affords a simpler notation. To obtain the 

 numbers per cubic centimeter the count made is simply multiplied by 60,000. 

 It has been found in practice that the number of yeasts and spores varies, 

 for Mo cubic millimeter, from practically none in home-made and first-class 

 commercial ketchups up to 100 or 200, and in one sample the number was as high 

 as 1200. Laboratory experiments show that, when the number of yeasts in raw 

 pulp reaches from 30 to 35 in J^o cubic millimeter the spoilage may frequently 

 be detectable by an expert by odor or taste, and from experiments made under 

 proper factory conditions, it seems perfectly feasible to keep the number in 

 commercial ketchups below 25. 



ESTIMATION OF BACTERIA 



The bacteria are estimated from the same mounted sample as that used for 

 the yeasts and spores. A power of about 500, obtained by using a high-power 

 ocular, is employed in this case, and because of the greater number present a 

 smaller area is counted over. Usually the number in several areas, each con- 

 sisting of five of the small-sized squares, is counted and the number of organisms 

 per cubic centimeter is calculated by multiplying the average number in these 

 areas by 2 ,400,000. Thus far it has proved impracticable to count the micrococci 

 present, as they are likely to be confused with other bodies frequently present in 

 such products, such as particles of clay, etc. A comparison of this method with 

 the ordinary cultural methods on samples in which the organisms had not been 

 killed has almost invariably shown that the one used gives too low instead of too 

 high results. In some cases it was found to give not more than one- third of the 

 entire number present. The estimates of the laboratory on this point may, 

 therefore, be considered very conservative. 



As regards the limits which may be expected in the examination of ketchups 

 for bacteria, it might be stated that some manufactured samples as well as good, 

 clean products made by household methods, have been examined, and the count 

 found to be so low when estimated by this method that the numbers present were 

 reported as negligible. In other words, it was found that for the areas counted 

 over, the number of bacteria averaged less than one that is, less than 

 2,400,000 per cubic centimeter. It is unusual, however, for the final number 

 per cubic centimeter to be less than from 2,000,000 to 10,000,000 organisms. 

 Contrasted with this number as a minimum, it has been found that the number 

 has occasionally exceeded 300,000,000 per cubic centimeter. Such a number as 

 this would indicate extremely bad conditions and carelessness in handling, as the 

 studies of factory conditions has shown that there is little excuse for the number 

 ever exceeding 25,000,000 per cubic centimeter. While experiments have also 

 shown that although the effect produced by the bacteria on the product varies 

 with different species, it is true that their presence can frequently be detected 

 in the raw pulp by odor or taste when the number exceeds 25,000,000 per cubic 

 centimeter and sometimes when the count is as low as 10,000,000. 



To one who has not been initiated into the mysteries of the microscope the 

 presence of such a number of bacteria in a food product seems inexcusable. It 



