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 lesions were placed via bilateral microinjections of 30 nmol / 200 nl N - methyl - D - aspartic acid .
### Output Text:
The lesions were placed via bilateral microinjections of 30 nmol / 200 nl <span class="chemical">N - methyl - D - aspartic acid</span> . 