Thoma cell counting chamber

The frame of the counting chamber contains a large central square (with a 1 mm² which can be seen in its entirety with the 10X objective.

This large central square is divided into 16 medium squares (with the 40X objective the medium squares can see completely), each with 25 small squares inside (9 of them are divided in half) .

. When we put the sample under the coverslip, the cell suspension reaches a height of 0.1 mm. Taking these data into account, and considering one of the large squares, the volume will be:

1 x 1 x 0,1 = 0,1 mm³ = 10^-4 ml

With the 10X objective of the microscope the counting area must be located. To count the cells the microscope must be switched to 40X objective. All the cells in the 16 medium squares must be counted according to the following criteria:

All the cells within each medium square and those that are over the top and right sides of the square (even when they are partially out) are counted. Following this approach, in the figure the cells in green will be counted, but not the cells in red.

If we have counted N cells in one of the large squares (that is, in 16 medium squares), the concentration of our sample will be:

N x 10⁴ cel/ml

When prior to counting we concentrated or diluted the initial sample, we must take into account the concentration-dilution factor (f):

N x 10⁴ x f cel/ml

suspensión celular inicial = suspensión celular diluida x factor de concentración-dilución