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: This was accompanied by a lower activity of N - acetyl - beta - D - glucosaminidase , together with a decrease of lipid peroxidation and increase of antioxidant systems .
### Output Text:
This was accompanied by a lower activity of N - acetyl - beta - D - glucosaminidase , together with a decrease of lipid peroxidation and increase of antioxidant systems . 