Flagellants mortifying the flesh, at the time of the Black Death
Mortification of the flesh literally means "putting the flesh to death". The term is primarily used in religious contexts, and is practiced in a variety of ways.
In its simplest form, it can mean merely denying oneself certain bodily pleasures, such as by abstaining from chocolate, from meat, from alcohol, or from sex. It can also be practised by deliberately choosing a simple or even impoverished lifestyle; this is often one reason many monastics take vows of poverty.
In some of its more severe forms, it can mean actually inflicting pain and physical harm to oneself, such as by beating, whipping, or other means. Some psychologists associate this practice with algolagnia.
It has been speculated that the more extreme practices of mortification of the flesh may be used to obtain altered states of consciousness for the goal of experiencing religious experiences or visions.
A portion of the body may die in consequence of the disturbance of its nutrition by inflammation, or of a cutting off of the bloodsupply, as by pressure upon, or injury to, the blood-vessels.
This is apt to be met with in oldish persons with diseased vessels and feeble heart-action, especially if the blood is rendered less nutritious by the presence of diabetes or of kidney disease.
The rule of treatment in all cases of threatened mortification is to keep the part warm by flannel or cotton-wool, but to avoid all methods which unduly hurry the returning circulation.
From this original use of the term, we see that mortification, though under one aspect it is a law of death, under another and more fundamental aspect it is a law of life, and does not destroy but elevates nature.
To this extent, mortification is obligatory on all, but those who wish to be more thorough in the service of Christ, carry it further, and strive with its aid to subdue, so far as is possible in this life, that "rebellion" of the flesh against the spirit which is the internal incentive to sin.
Mortification, viewed thus as a means of curing bad habits and implanting good ones, has its recognized place in the methods even of those who are engaged in pursuing purely natural ends.