def parse_keywords(medline):
    """Parse keywords from article, separated by ;

    Parameters
    ----------
    medline: Element
        The lxml node pointing to a medline document

    Returns
    -------
    keywords: str
        String of concatenated keywords.
    """
    keyword_list = medline.find('KeywordList')
    keywords = list()
    if keyword_list is not None:
        for k in keyword_list.findall('Keyword'):
            if k.text is not None:
                keywords.append(k.text)
        keywords = '; '.join(keywords)
    else:
        keywords = ''
    return keywords