Digitonomy:
Does Canon 18 of the
Fourth Lateran Council remain in effect, or have these rules been superseded by newer regulations on this topic?
The tools of surgery (cutting, burning) and the means to alleviate pain have come a long way since the Lateran Council and so has the reputation of those practicing medicine. In part the Lateran legislation reflected a desire to not bring disrepute on the clergy.
However, earlier universal disciplinary laws such as this one which were not contained explicitly or implicitly in the 1917 code were abolished when it was issued (CIC 1917 c. 6). Yet, canon 139 §2 of the 1917 code required an apostolic indult for a cleric to be a surgeon or physician.
With the 1983 code though, the 1917 code itself was abrogated, and the subject matter of the former canon was completely reordered. On the basis of canon 6 in the new code, the prohibition ceased to be universal law.
Today, the means to regulate this would arise from canon 285 of the new code:
“§1. In accord with the prescriptions of particular law, clerics are to refrain completely from all those things which are unbecoming to their state. §2. Clerics are to avoid those things which, although not unbecoming, are nevertheless alien to the clerical state.”
So while universal law doesn’t prohibit clerics from these professions, a diocesan bishop, for example, could make a law for his diocese that would prohibit them, or he could forbid a particular cleric. He could believe there is a just cause to allow it in a particular case, and he does has the right and authority to assign his clergy, who are bound to obey his legitimate commands.
In point of fact, a number of permanent deacons do exercise medicine in their secular professions today, and this is totally lawful. It adds a special dimension to the healing arts they practice.
I do think the possibility that a bishop would permit a priest to do this is low however, since priests exercise the functions of ministry on a full time basis. They should be about the business of healing souls.
The subdiaconate, of course, has been suppressed in the Latin Church for a number of years. One becomes a cleric, not by tonsure as was formerly done, but by ordination to the diaconate.