The Energy needed to acquire Immune Response cards is generated in two ways:
• by Crystals on Stomach cards currently in the Digestive Tract, and
• by playing cards from your hand.
To calculate how much Energy you are able to generate, first count all the Crystals in the Tract. Each Crystal provides 1 Energy.
Then, you may play Stomach cards not containing Crystals from your hand face up in front of you in order to gain the remaining required Energy. Each card you play provides 1 Energy.
Any card played from your hand to gain Energy is then placed at the bottom of the Stomach deck, in any order you choose.
IMPORTANT: YOU MAY NOT PLAY CARDS WITH A CRYSTAL TO GAIN ENERGY.