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 authors conclude by affirming the undoubted efficacy of the anabolizing steroids in experimental myopathic disease , but they have reservations as to the transfer of the results into the human field , where high dosage cannot be carried out continuously because of the effects of the drug on virility ; because the tissue injury too often occurs at an irreversible stage vis - a - vis the " regeneration " of the muscle tissue ; and finally because the dystrophic injurious agent is certainly not the lack of vitamin E but something as yet unknown .
### Output Text:
The authors conclude by affirming the undoubted efficacy of the anabolizing <span class="chemical">steroids</span> in experimental myopathic disease , but they have reservations as to the transfer of the results into the human field , where high dosage cannot be carried out continuously because of the effects of the drug on virility ; because the tissue injury too often occurs at an irreversible stage vis - a - vis the " regeneration " of the muscle tissue ; and finally because the dystrophic injurious agent is certainly not the lack of <span class="chemical">vitamin E</span> but something as yet unknown . 