The word hematologist comes from the Greek word haimo (blood) and the Latin word logia (the study of).  The term "hematology" was first recorded between 1805 and 1815. 

For those of you that are old enough, you may have seen the film "Hemo the Magnificent" when you were in school.  It told all about the circulatory system.  

Just to add a some bits, to what Bill W has said,

a few more facts:

What is a Hematologist? (Blood Disorder Specialist)

Our linguist friend @Myr has done it again

And he’s trying to explode my poor brain

So he adds to the list

Another damn -ologist

Just to keep my blood boiling in vain