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: Response to Varidase skin test antigen was negative for all eight tuberculosis patients tested , but there occurred a hyper - responsiveness of the lymphocytes of these eight patients to phytomitogen ( PHA - P ) . as well as of those of seven other tuberculous patients .
### Output Text:
Response to Varidase skin test antigen was negative for all eight tuberculosis patients tested , but there occurred a hyper - responsiveness of the lymphocytes of these eight patients to phytomitogen ( PHA - P ) . as well as of those of seven other tuberculous patients . 