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: It is assumed that patients with some cerebral damage are liable to manifest DPH toxicity as focal neurological signs .
### Output Text:
It is assumed that patients with some cerebral damage are liable to manifest <span class="chemical">DPH</span> toxicity as focal neurological signs . 