In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Functional evidence relating the IC to motor behavior derives from experiments showing that activation of the IC by electrical stimulation or excitatory amino acid microinjection causes freezing , escape - like behavior , and immobility .
### Output Text:
Functional evidence relating the IC to motor behavior derives from experiments showing that activation of the IC by electrical stimulation or excitatory <span class="chemical">amino acid</span> microinjection causes freezing , escape - like behavior , and immobility . 