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: METHODS : Twenty - six renal allograft biopsy specimens from 1 9 renal transplant patients who underwent transplantations between 1991 and 1993 were evaluated .
### Output Text:
METHODS : Twenty - six renal allograft biopsy specimens from 1 9 renal transplant patients who underwent transplantations between 1991 and 1993 were evaluated . 