150294
In 1849 he succeeded Ignaz Semmelweis as assistant to professor Johann Klein at the hospital 's first maternity clinic , a position he held until 1853 .
 Ignaz Semmelweis, Johann Klein
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Ignaz Semmelweis, Johann Klein