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The general notion of the application of engineering to medicine can be traced back centuries ; for example , Stephen Hales 's work in the early 18th century which led to the invention of a ventilator and the discovery of blood pressure certainly involved the application of engineering techniques to medicine .
 person: Stephen Hales
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 person: Stephen Hales