I would like to know where the title "improvement in drill-bit" came from in US38119, the applicant or the USPTO. Nowhere in the text does the applicant refer to the device as a drill-bit.
In general, a patent examiner may suggest or require an applicant to change the title of a patent in order to make it more descriptive of the claimed invention.
606.01 Examiner May Require Change in Title [R-11.2013]
Where the title is not descriptive of the invention claimed, the examiner should require the substitution of a new title that is clearly indicative of the invention to which the claims are directed. Form paragraphs 6.11 and 6.11.01 may be used.
In this particular case, given the age of the patent, it is probably pretty difficult to determine whether the title was changed. A twist drill is a type of drill bit, so the title may have been changed to make the patent easier to search. (Especially since at the time searching would have involved leafing through paper copies in a filing cabinet.)