What is the meaning of Yi Qi in Bu Zhong Yi Qi Tang?

Buzhong Yiqi Tang is a formula that was described in an important text of the Chinese tradition, the Pi Wei Lun (Treatise on Spleen and Stomach, 1249 A.D.), which is available in English translation (1). Its author, Li Gao (also known as Li Dongyuan) was considered the leader of the Spleen/Stomach School, a movement within the evolving ancient tradition that focused on deficiency of spleen and stomach as the origin of numerous diseases. This was one of four leading schools of thought that developed during the Chinese medicine reforms of the Jin-Yuan Dynastic period.