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: The activities of the lysosomal enzymes acid and neutral protease , N - acetylglucosaminidase , and acid phosphatase were measured in the serum of patients with fulminant hepatic failure .
### Output Text:
The activities of the lysosomal enzymes acid and neutral protease , N - acetylglucosaminidase , and acid phosphatase were measured in the serum of patients with fulminant hepatic failure . 