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: Evidence is accumulating that lindane can be toxic to the central nervous system and may be associated with aplastic anaemia .
### Output Text:
Evidence is accumulating that <span class="chemical">lindane</span> can be toxic to the central nervous system and may be associated with aplastic anaemia . 