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: Parameters of study included analysis of serum chemistry ( ALT , BUN and CPK ) , and orderly fragmentation of genomic DNA ( both endonuclease - dependent and independent ) in addition to microscopic evaluation of damage and / or protection in corresponding PAS stained tissues .
### Output Text:
Parameters of study included analysis of serum chemistry ( ALT , BUN and CPK ) , and orderly fragmentation of genomic DNA ( both endonuclease - dependent and independent ) in addition to microscopic evaluation of damage and / or protection in corresponding PAS stained tissues . 