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: Improvement began within 3 to 6 months and consisted of cessation of active cutaneous lesions in all 7 patients , skin softening in 5 , and more normal growth of the affected limb in 2 of 3 children .
### Output Text:
Improvement began within 3 to 6 months and consisted of cessation of active cutaneous lesions in all 7 patients , skin softening in 5 , and more normal growth of the affected limb in 2 of 3 children . 