208 PHARMACEUTICAL BACTERIOLOGY 



recent years. Much of the material placed in cans and offered in the 

 market is of very inferior quality, being made from tomato refuse, trim- 

 mings and rotten tomatoes. Two methods of direct microscopical exam- 

 ination of these products are in use. 



a. The Howard or Bureau of Chemistry Method. The method con- 

 sists of three parts, as follows: 



Mold Counting. A bit of the tomato product (as catsup, puree, sauce, 

 paste) is placed on the special Howard mold chamber (depth 34 o mm.) 

 and covered with a thick cover glass. The counting is done by means of a 

 low power objective, the draw tube being so adjusted that the diameter 

 of the field of view is just exactly 1.83 mm. (therefore an area of about 

 2.5 sq. mm.). Each field showing mold hyphae extending ^ of the way 

 across, or more, is counted as positive mold. A tomato product is con- 

 sidered unsuitable for human consumption, if it shows 66, or more, per cent, 

 of the fields of positive mold. 



Spore Counting. The spore count includes mold spores of all kinds 

 as well as yeast cells and the counts are recorded as so many per %o 

 cubic mm. 



Bacterial Counting. The hemacytometer is used. Only the large 

 "rod shaped forms "are counted, it not being specified whether the 

 smaller forms and the diplobacilli are to be included. 



The Howard method has been severely criticized for several reasons. 

 It does not allow for differences in the consistency of the various tomato 

 products. The fact that only "rod shaped" bacteria are counted has 

 rendered the bacterial counting practically valueless as far as the protec- 

 tion of the consumer is concerned, since the distinctively rod shaped bac- 

 teria found in tomato products are mostly of the lactic acid forming group, 

 and largely harmless, whereas the coccus forms, streptococcus forms, small 

 diplobacillus forms, to which groups belong many of the filth and sewage 

 types, are not counted. There is also no excuse for the unusual fractional 

 recording of the spores and there should be a distinction made between 

 spores and yeast cells. In those laboratories not under the direction of 

 Federal and State pure food law administration, the Howard method is 

 modified so as to conform to other more scientific methods of foods exam- 

 ination. The defenders of the Howard method declare that the method is 

 purposely simplified in order to suit it to the capabilities of the analysts 

 who are employed to do the microscopical work in the various laboratories. 

 This argument is not worthy of serious consideration. Incompetent 

 analysts have no place in any laboratory, least of all in a laboratory where 

 matters affecting the public health are concerned. 



4. General Method for Making Direct Bacterial Counts. The follow- 

 ing method is practically applicable in the direct microscopical examina- 



