What evidence in a slice of bread showed the presence of gas?

Every slice of the bread, contains a number of blister like pores. These blister like pores suggests that the air or some gas might be present there. In case, the bread has no air, the surface of the bread must be smooth rather than rough.

The bread is formed by the fermentation of the sugar molecules present in the dough with the help of yeast. These blisters like structure on the bread is present due to the gas produced during fermentation.