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: Production of autochthonous prostate cancer in Lobund - Wistar rats by treatments with N - nitroso - N - methylurea and testosterone .
### Output Text:
Production of autochthonous prostate cancer in Lobund - Wistar rats by treatments with <span class="chemical">N - nitroso - N - methylurea</span> and <span class="chemical">testosterone</span> . 