Counting the number of cells in a suspension is a process that involves the use of a stain. For instance, when trypan blue is used, it penetrates the cell membrane of the dead cells, but not the living cells.
The cells are then gently expelled into a haemocytometer (contains the counting chamber) under the cover slip and observed under a microscope. Cells are then counted within a given number of squares for calculations.
This method is largely preferred due to the fact that it allows for cells to be suspended in a solution rather than being held in a solid media. Here, therefore, it becomes easier to manipulate the contents thereby preventing them from forming clusters. With cell suspensions, it’s also easier to observe single cells under the microscope.
In this case, it becomes possible to not only study the structure of the cells, but also get to observe how well they have differentiated; viewing dead and living cells under the microscope.