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: Four out of 23 consecutive patients treated with high - dose Ara - C for lymphomas in our institution developed a strikingly similar syndrome during the perfusion .
### Output Text:
Four out of 23 consecutive patients treated with high - dose <span class="chemical">Ara - C</span> for lymphomas in our institution developed a strikingly similar syndrome during the perfusion . 