In estimating the number of yeasts and spores in pulp or ketchup, the Thoma-Zeiss counting chamber is used and the mount observed under a magnification of 180 diameters. To prepare the sample, 10 cc of the material has 20 cc of water added and is “thoroughly mixed.” Before taking a drop for examination, the sample is allowed to rest for a “moment” to allow the “coarsest particles” to settle. This step in the technique is not as clear as could be desired, for what might be considered as “thoroughly mixed” by one microscopist as a half dozen shakings of the cylinder, might not be so construed by another even with sixty shakings. As the material consists of both solids and liquid, this is a very important detail, as it may easily account for some of the wide differences in results obtained by different workers on the same sample. In a bulletin[2] dealing with the examination of solid foods, the following statement occurs relative to the shaking in order to be able to obtain the bacterial condition: “The longer the shaking, the more perfect was the diffusion of particles. It could not, however, be continued beyond a comparatively short period of time, because of the multiplication of organisms. With the quantities of tissue above stated, ten minutes’ shaking was selected as a happy medium between an undesirable multiplication of the organisms on the one hand and the retention of the organisms by the tissue and the consequent lowering of the numbers found, on the other.” The organisms in pulp or ketchup are dead, or, if alive, do not possess such phenomenal power of multiplication, therefore, the shaking should be conducted with sufficient energy and for a sufficient time to insure their separation from the tissue. Furthermore, “letting stand for a moment” may mean thirty seconds or two or three minutes to different persons. ----- Footnote 2: No. 115—Bureau of Chemistry, Dept. of Agr.