. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . Fig. 51. — Coloniescircular in form, com-posed of radiatingthreads. Fig. 52. — Colonies withopaque centres, with a thinborder fringe. Fig. 53.—Colony showinga network of threads whichis thicker in the centre. full development, some of the colonies become confluent, and some of the feeblerbacteria are checked in their development by the crowding and do not developcolonies. The plate that shows about 100 colonies is chosen, therefore, forcounting. When no one plate is completely satisfactory in numbe
. Pathogenic microörganisms; a practical manual for students, physicians, and health officers . Fig. 51. — Coloniescircular in form, com-posed of radiatingthreads. Fig. 52. — Colonies withopaque centres, with a thinborder fringe. Fig. 53.—Colony showinga network of threads whichis thicker in the centre. full development, some of the colonies become confluent, and some of the feeblerbacteria are checked in their development by the crowding and do not developcolonies. The plate that shows about 100 colonies is chosen, therefore, forcounting. When no one plate is completely satisfactory in number and even CVLflVAflON OF MICROdRGANISMS llV distribution of the colonies, two of the nearest satisfactory plates are countedand the results averaged. Whenever possible all the colonies on a plate shouldbe counted. Where the colonies are crowded it is necessary to divide the plateinto sections to facilitate counting. This is best done by placing the Petri. Fig. 54.—Photograph of a large number of colonies developing in a layer of gelatincontained in a small Petri dish. Some colonies are only pin-point in size; some as large asthe end of a pencil. The colonies here appear in their actual size. dish on a Wolffhtigel counting plate, which is a glass plate ruled in squarecentimeters, some of the squares being still further divided into 9 small row of squares is counted and then a row at right angles to the first, to obtaina fair average. The number of colonies is divided by the number of squarescounted. If the usual 10 Petri dish is used, the number per square centi-meter is multiplied by 63, the number of square centimeters on the dish, to
Size: 1572px × 1589px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookauth, bookcentury1900, bookdecade1910, bookidcu31924000235212
