Although it is not necessary to do so, we can make a simplifying assumption that both human cells and bacterial cells have the shape of cubes. Since the bacterial cells are I /25th the length of the human one, as many as 25 x 25 x 25 will fit inside. (Picture a large cube and start stuffing it with the little ones, 25 rows of 25 on the bottom layer, and 25 such layers); 25 x 25 x 25 =15,625. Since we are estimating, we should round off to about 16,000. We will later see that this consideration of bacterial cells fitting within human cells is not without significance, both in terms of mitochondria and chloroplasts and in terms of our immune systems.
