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: Results described here demonstrate that this agent does in fact induce pathogenic t ( 9 : 22 ) translocations in a human myeloid cell line in vitro , but does so at low frequencies .
### Output Text:
Results described here demonstrate that this agent does in fact induce pathogenic t ( 9 : 22 ) translocations in a human myeloid cell line in vitro , but does so at low frequencies . 