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: CONCLUSIONS : The results of our study show that even after a single bolus , mannitol may leak through the altered BBB near gliomas , reversing the initial plasma - to - blood osmotic gradient , aggravating peritumoral edema and promoting rebound of ICP .
### Output Text:
CONCLUSIONS : The results of our study show that even after a single bolus , <span class="chemical">mannitol</span> may leak through the altered BBB near gliomas , reversing the initial plasma - to - blood osmotic gradient , aggravating peritumoral edema and promoting rebound of ICP . 