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: We selected the 54 ( 30 . 5 % ) cases of immediate AX allergy with good tolerance of PG .
### Output Text:
We selected the 54 ( 30 . 5 % ) cases of immediate <span class="chemical">AX</span> allergy with good tolerance of <span class="chemical">PG</span> . 