Beitza 18 a, b

What an added joy to learn about halachot for Festivals during a Festival!  Though the learning was not directly relevant to my experience over the past few days, I appreciate the rabbis' search for ways to express our joy without violating any restrictions.

Today we review a number of concepts and principles.  The topic is ritual immersion on a Festival: is this allowed?  Under which circumstances?  Using what reasoning?

Steinsaltz offers a quick review of the rules of ritual impurity.  He reminds us that ad hatuma, primary ritual impurity, will impart ritual impurity to people, vessels, food and drink.  Any of these objects that become ritually impure are now velad ha terumah - derivative sources of impurity.  A corpse is the ultimate source of ritual impurity.

Items that are velad hateruma can impart ritual impurity only to food, drink or consecrated items.  Food that is velad hateruma cannot impart ritual impurity to any other items.  However, velad hateruma does invalidate teruma, and so priests must know whether their food has come into contact with second degree ritual impurity.  To clarify: any item that has become impure through contact with a velad hateruma is also said to have second degree impurity.

Much of the daf wonders whether we can immerse items in ritual baths - including women ending their menstrual cycles - on Yom Tovim or Shabbatot.  The rabbis question different items and their degrees of ritual impurity.  They are careful to evaluate whether or not an action might be violating a halacha related to Shabbat.  For example, we are not allowed to bathe on Shabbat.  Is immersing a form of bathing?

Of particular interest to me were two items related to this immersion.  One regards women who do not bring a change of clothing to the mikvah.  Should they be allowed to "employ an artifice" and immerse while wearing their clothing? During a Festival?  The second regards a person who immerses in a bath not to wash not to affect his/her ritual status but to cool down on a hot day.  Is this always allowed?

These questions (among others) bring us to the principle of ho'il, since.  Ho'il helps us to understand how context might affect one's actions and whether those actions are halachically sound.  For example, if a person is permitted to bathe in foul smelling water on a hot day simply to cool down and not for pleasure, bathing nor for ritual immersion, should we not allow another form of immersion in water under other circumstances?

Another argument used regards using vinegar on Shabbat to ease gum pain.  We are not permitted to use items primarily for their medicinal qualities on Shabbat.  However, we are certainly permitted to ingest vinegar as food.  Thus we can dip bread in vinegar and eat it in a usual manner on Shabbat - and if we benefit medicinally from that vinegar, that is perfectly fine.  

Some of the other complicating factors in determining whether or not immersion is permitted on Festivals involves the status of the item to be immersed, the status of the water itself, the status of the vessel holding the item to be immersed, the timing of the immersion and the day in question (Shabbat, Yom Tov, 9th of Av, etc.).

Clearly this daf is beyond my current ability to comprehend.  At the same time, its clarity helped me to better piece together a number of important Talmudic principles/concepts.