Oxford English Dictionary citation of Gaddis for use of "internes" in The Recognitions,
from p.1121 INTERMUSCULAR-INTERNAL in the compact edition of the OED, under intern (a. and sb.).

B. sb. Also interne. 'An inmate as of a school; especially an assistant resident physician or surgeon in a hospital, usually a student or recent graduate, acting in the absence of the attending physician or surgeon.' ('A recent use from Fr.', Cent. Dict.). Now usu. , a recent medical graduate who is working under supervision in a hospital (and often living there) as part of his training, prior to entering general practice or becoming a resident. (Broadly equivalent to a houseman in Great Britain) Also trans., used of individuals in other professions who are receiving practical experience under supervision. Chiefly U.S.

Prior users of "interne" include Lister & William James; Gaddis is the seventh instance given:

1955 W. Gaddis, Recognitions I. i. 41 Physicians, technicians and internes X-rayed the boy from every possible angle.

from Daniel Beraca Visel