In 1936, Dr. Mayer-Wegelin published an excellent book on pruning (Mayer- Wegelin, H. 1936, Astung. M. & H. Schaper, Hannover). 
    The book outlines the different periods of pruning in Europe.  The book explains the branch protection zone and the controversies on how to make the pruning cut.  I am including here only a few excerpts.  People who are really interested in pruning will find this book of extreme value.  An English translation is in the United States Forest Service Library as Translation 364.

EXCERPTS

    In the past German foresters twice have had recourse to pruning to a large extent, at first in the 18th century and then in the last third of the 19th century.  Twice a period of intense pruning was followed by a reactionary period, a more or less prolonged period, during which pruning fell into disrepute and oblivion.

    Pruning, however, in the 18th century was no innovation.  It was prescribed in the various forest ordinances of the 16th century, mentioned in "Hausvater" literature and discussed in Carlowitz's "Wilde Baumzucht" (Wild Silviculture).  In France and Belgium pruning was highly developed as a specialty of a separate craft guild.

    Not only was there a good deal of pruning but "never had pruning been done so badly as in those days",

    For many subsequent decades there prevailed among foresters an intense distrust of pruning in general.

    In this respect the treatise on pruning by De Courval opened up new ways.  Instead of the old removal procedure of stumping the branches of oak trees, a method that led to the rotting of the stems, he introduced a new procedure of removing the branches smoothly and closely to the stem and protecting the wounds immediately by putting on a thick layer of tar.

    In forest literature there has been considerable dispute as to whether pruning should occur in front of the swelling or through it.

    In the base of the dead hardwood branch the dead wood is almost always clearly separated from the living wood which is nourished laterally from the stem.  "A dark, narrow strip indicates the boundary."  "A cross section through the base of a dead beech branch clearly shows a definitely defined, narrow, reddish-brown separating layer between the outer dead part and the inner portion of the branch which is still full of sap and green."

    The formation of the protective layer begins in the cambium of the branch and penetrates from the outside toward the pith.  It depends on the presence of living cells.  

    One question has been discussed frequently in pruning literature, namely, whether the pruning cut should occur through the swelling at the branch base or immediately above it.  After Buchting had made the demand in 1756 that the branch should be cut "just above the curled ring", the question has been touched upon in many publications.  Almost all of the numerous authors decided in favor of sawing through the branch swelling and base this on the fact that the wound heals over more rapidly when the cut goes through the swelling, even if the wounded surface itself is larger than when the cut occurs above the swelling.

    Therefore, to bring about as early a healing as possible the most practical cut should go through the swelling at the base of the branch.  In literature this pruning regulation is supplemented by another requirement, namely, that the pruning cut should be made close to the stem but not too close, that is, "just above the annual ring around the base of the branch."

In 1756 Buchting said that the branch collar should not be injured or removed.  Many tree workers have said the same words for centuries.  Yet, the collars were cut and the protection zones were destroyed.  Why?  Because large "callus"- woundwood-ribs were considered a sign of healing.  And, that wood is dead.  And, wound dressings will stop rot.  These problems are still with us today.