This paper is a critical review of the "drop piate" method of determining the number of viable bacteria in fluids, together with a description of an experimental comparison of the "drop plate" with the more usual "pour plate" procedure.It is shown that counts on pure cultures of bacteria made by the "drop plate" method are some 7 /6 higher than those made on the same cultures by the "pour plate" method. It is also shorvn that the standard error of a series of counts made by the "drop plate" procedure is slightly less than for those made by the "pour plate" method.A successful "drop plate" method of determining the number of viable bacteria in fluid suspension has been in use for a number of years in several English research laboratories. Considerable experience with the method suggests the desirability of reviewing the procedure both as a research tool and for routine assays of such material as milk.Donald (2) introduced a method for the precise measurement of fluid volume by means of drops. This depends upon the fact that the size of a drop delivered from a pipette is governed, other factors being constant, by the erternal diameter of the dropping tube. Fildes and Smart (3) expanded the procedure and developed methods of preparing and calibrating the pipette. Several authors have described in brief form the adaptation of dropping pipettes to the technique of plate counts of bacteria, particularly Wilson (9), Aitken, Barling, and Miles (1), Kenny, Johnston, von Haebler' and Miles (5), von Haebler and Miles (4), Miles, Misra, and Irwin (7), and Snyder (8). The last two papers include a statistical analysis of the accuracy of the method.The plating procedure consists simply in adding, with a calibrated dropping pipette, drops of properly diluted suspensions of bacteria to the surface of nutrient agar or other appropriate medium in Petri plates. The surface of the medium must be dried to the stage where a drop of bacterial suspension will spread over an area of 1.5 to 3 cm. in diameter and permit absorption of the fluicl of the drop in 15 to 20 min. On incubation the area covered by a drop of suitably diluted suspension will develop well spaced surface colonies that permit rapid and accurate counts. Droppi,ng PipettesThese are made, as described glass tubing to form two pipettes Methods by Donald, by drawing a length of 7 mm. rvith long, very gradual tapers.
A chromatographic method for the qualitative and rough quantitative estimation of sugars and soluble phosphates in plants is described. Using this method, representatives of 27 families of Spermatophyta and 10 representatives of Algae have been examined. In Spermatophyta the total sugar content was found to be fairly high, with sucrose usually the main sugar, and glucose predominating over fructose. In Chlorophyta, the concentration and the nature of the sugars present were fairly similar to those in Spermatophyta. In Phaeo-phyta, Rhodophyta, and a diatom Nitzschia, the soluble sugar content was very low, with glucose usually being the main sugar. The distribution of sugars in aquatic Spermatophyta was similar to that of terrestrial Spermatophyta rather than that of Algae. When wheat leaves were detached and placed on water in darkness, subsequent metabolism of their sugars was found to be markedly affected by the conditions of illumination prior to leaf detachment. On illumination, detached wheat leaves accumulated large amounts of alcohol soluble fructosans, while attached leaves did not. In detached wheat leaves during prolonged starvation, soluble phosphates, both organic and inorganic began to accumulate after two days, indicating breakdown of some insoluble forms of phosphorus. By this time free sugars had completely disappeared, though sucrose reappeared in relatively large amounts on the third day and then declined again.
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