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He then studied under Ludolf von Krehl and earned the degree of doctor of medicine in Heidelberg in 1911 .
 Ludolf von Krehl, Heidelberg
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 Ludolf von Krehl, Heidelberg