Dear Prof. Kestane Sevil

In the Thoma counter, the frame of the counting chamber contains a large central square which can be seen in its entirety under the 10X objective.

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

All the cells that lie within each medium square (even when they are partially out) are supposed to be counted. You should count the cells per square and sum up all the 16 squares. Each sample may be counted three times in this manner, and you may take the average to calculate the original concentration.

After having taken the average count (say average count A), you may use the following formula.

Cell count= A x 10^4 cells/ml.

Prior to counting, if you have diluted the initial sample, then you must consider the dilution factor (say D). Suppose you have diluted the original sample 10 times (sometimes, you may have to dilute the sample if the cell concentration is too high as it becomes difficult to count), then the dilution factor D=10.

So, the cell count in the original sample would be

A x 10^4 x D cells/ml.

You have counted 600 cells (assuming that you have taken a total count of all the 16 squares without diluting the original sample), then you could calculate your original cell concentration by using the above formula,

Cell count= 600 x 10^4 cells/ml.

= 6 x 10^6 cells/ml.

Regards,

Malcolm Nobre