4 TOMATO KETCHUP UNDER THE MICROSCOPE. 



pressing the liquids out, which gives a very uneven appearing prepa- 

 ration. When a satisfactory mount has been obtained, it is placed 

 under the microscope and examined. The power used is about 90 

 diameters, and such that the area of substance actually examined in 

 each field of view is approximately 1.5 sq. mm. 



A field is examined for the presence or absence of mold filaments, 

 the result noted, and the slide moved so as to bring an entirely new 

 field into view. This is repeated till approximately 50 fields have 

 been examined, and the percentage of fields showing molds present 

 are then calculated. Our experience has demonstrated that for 

 homemade ketchups this is practically zero, and with some manu- 

 factured ketchup it is as low as from 2 to 5 per cent, while for care- 

 lessly made products it may be 100 per cent ; that is, every field would 

 show the presence of mold. Investigations under factory conditions 

 clearly indicate that with only reasonable care the proportion of 

 fields having molds can be kept below 25 per cent. A specimen in 

 which 60 per cent of the fields have molds is in more than twice as 

 bad a condition as one containing 30 per cent. 



After the percentage reaches 30 to 40 per cent it will be found 

 that some of the fields frequently have more than one filament or 

 clump of mold, and the number of such fragments might be counted, 

 but in this laboratory this usually is not done. A Thoma-Zeiss count- 

 ing cell with a center disk of 0.75 inch instead of 0.25 inch, as usually 

 furnished, would give a regular depth of liquid and would be more 

 exact than the method described, but this must be specially manu- 

 factured, not being listed in any of the catalogues of microscopic sup- 

 plies, and the method as given is sufficiently accurate for the purpose. 

 When the number of fragments of mold per cubic centimeter is 

 estimated, it has been found to range from virtually zero to over 

 20,000. There is no excuse for a manufacturer allowing such condi- 

 tions to prevail that his ketchup shows more than 2,000 per cubic 

 centimeter, while some manufacturers by careful handling hold it 

 down to 150. 



ESTIMATION OF YEASTS AND SPORES. 



Though the spores referred to are those coming from molds and 

 correspond to seeds in more highly developed plants, it is frequently 

 very difficult to differentiate some of them with certainty from some 

 yeasts without making cultures, which is obviously impossible in a 

 product that has been sterilized by heat. For this reason the yeasts 

 and spores have been reported together, and if there seemed to be a 

 larger percentage of the latter, mention was made of that fact. 



To make a count 10 cc of the product is thoroughly mixed with 

 20 cc of water, and after being allowed to rest for a moment to permit 

 the very coarsest particles to settle out, a small drop is placed on the 

 central disk of the Thoma-Zeiss counting cell and then covered with 



