| Popis: |
IN this paper a short account is given of the application of photo-electric methods to bacteriology. Although such methods are now well established, and have been used in colorimetry and nephelometry for some years, they have not received the attention they deserve. The apparatus required, apart from the cell, will be found in any well-equipped laboratory; and their simplicity, as well as the elimination of personal errors, should assure the use of such methods in all experiments involving the measurement of colour intensity or turbidity of fluids. The estimation of the number of organisms in a broth culture by methods in common use is laborious and subject to gross error. These methods have been summarised and criticised recently by Gardner (1931), and the errors found vary between 10 and 50 per cent. The time consumed in a single estimation also varies greatly; and, when organisms are counted directly in a counting chamber, is considerable. During the past few years experiments have been carried out to devise a method whereby such estimations could be performed accurately and instantaneously, in a growing culture, without the intervention of the factor of personal error. For this purpose many types of light-sensitive cells, and many variations in technique and arrangement have been investigated. These will be summarised, and the final arrangement, which has been entirely satisfactory, will be described in detail. The principle was in all cases the same. It involves the use of a lightsensitive cell as a nephelometer. Such a system demands a constant light source, a cell of great sensitivity, of linear response to varying light intensities, and no "lag" or "tiring" properties. In addition, a sensitive recording instrument is essential. |
