QUANTITATIVE MICROSCOPIC DETERMINATIONS 145 



A SODA FOUNTAIN FRUIT 



Total bacteria 250,000,000 per cc. 



Total yeasts 40,000,000 per cc. 



Fragments of mold hyphae 50,000 per cc. 



After some of the fruit product had been incubated in a clean 

 sterilized beaker for four days at a temperature of 37C. it had under- 

 gone total decomposition (100 per cent, decomposition), represented, 

 let us suppose, by the following counts: 



COMPLETELY DECOMPOSED PRODUCT 



Total bacteria 3,000,000,000 per cc. 



Total yeasts 150,000,000 per cc. 



Mold hyphaj 2,000,000,000 per cc. 



Since a substance cannot be decomposed 300 per cent., we must 

 consider each count at 100 per cent., add and divide by three. Con- 

 sidering first the bacterial counts, we find that 2 %joo times 100 per cent, 

 equals 8.3 per cent., (that is, 250,000,000 :: 3,000,000,000 :: x : 100 

 per cent.). As to the yeasts we have f 5 times 100 per cent., or 26.6 

 per cent. The mold count in the original as compared with the com- 

 pletely decomposed material is negligible, amounting to a very small 

 fraction of 1 per cent., and may be considered as zero. 8.3 + 26.6 

 + 0-7-3 = 11. 6 per cent, decomposition of the fruit product, of 

 which yeast decomposition was preponderant. . In another product the 

 several kinds of decomposition may be quite different in kind as well 

 as in degree. These estimates are approximate only, but are entirely 

 practical. The analyst must remember to make the culture of the 

 substance under examination without any additions or modifications 

 of any kind. If the material contains vegetable tissues and cell 

 elements in coarser aggregates, a small well mixed bit of the material 

 to be examined should be rubbed through a wire 100 mesh sieve, and 

 likewise a bit of the completely decomposed material. This must be 

 uniformly done in order that the results of the counts may be uniform. 



3. A Microscopical Standard for Pyrethrum Insect Powders. Ac- 

 cording to Insecticide Decision No. 1, by the U. S. Department of 

 Agriculture under date of July 15, 1911, the term " insect powder," 

 when used without qualification, means an insecticide made from the 

 powdered flower heads of Chrysanthemum (Pyrethrum) cineraricefolium 

 (Trev.) Bocc., Chrysanthemum (Pyrethrum) roseum Web. and Mohr, 

 and Chrysanthemum marshalli (Pyrethrum carneum M. B.) Ashers. 

 The terms "Pyrethrum" and " Pyrethrum powder" are, when applied 

 to insecticides, synonymous with "insect powder." In designating a 

 mixture of powdered flowers and stems, the term "insect powder" 

 may be used, provided this is immediately qualified by word or phrase 

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