| Nazir
 
After discussing the general topic of nedarim, vows, the Mishna moves to a most specific form of a vow, that of a nazir. The nazirite who takes a vow forbidding the consumption of grape produce, the taking of haircuts and contact with the dead is a rare phenomenon today. (The only nazir I am aware in recent times was Rav David Cohen, perhaps the primary disciple of Rav Kook). With no possibility of bringing sacrifices today - a necessary condition to end the status of nezeeroot -becoming a nazir today would be a lifelong commitment. This is in sharp contrast to the general thirty-day time frame of a "regular" nazir.
 
The Mishna does discuss two types of life-long nezeeroot, known in rabbinic parlance as a nazir olam and a nazir Shimson, the latter for one who takes a vow to be like the Biblical Nazir of the same name. The difference between the two is that a nazir olam may trim his hair if it becomes uncomfortable and should such a nazir accidentally come in contact with a dead body would be obligated to bring the three sacrifices that a regular nazir has to bring in such a situation.

One might have thought that the bringing of such sacrifices is not necessary for a nazir olam as these sacrifices restart the counting of the days of the nazir vow - a vow which must be completed in succession without contact with the dead. Since for a nazir olam  there is no start or end date to the nezeeroot one might have thought the bringing of sacrifices which re start the count would not be necessary. And in fact a nazir Shimshon need not bring sacrifices if he comes in contact with the dead. Nor can he trim his hair (or beard in the case of a male nazir[1]). Apparently a nazir Shimshon is one long nezeeroot lasting one's entire days whereas a nazir olam is one who is obligated in a series of nezeirot with a new cycle starting when as the prior one ends.
 
It is only contact with with death that necessitates a restart of the nezeerot. If a nazir were to drink wine or cut his hair he would be in violation of a biblical prohibition but that would not cancel the nezeeroot.

While for all practical purposes the laws of nazir are no longer applicable reading the Mishnayot leaves one with the impression that such was quite common in Talmudic times. People took vows of nezeeroot when they had children, when their friends did, as a way to fight alcoholism, in times of danger. The Gemara even recommends that one take a vow of nezeeroot when faced with a sexually promiscuous society.
 
Masechet Nazir discusses the technical details and nuances of the laws of nezeeroot. The Mishna opens up with a discussion of what exactly constitutes a vow of nezeeroot. If people were to speak clearly and directly there would be little problem but all too often such is not the case (an art perfected by diplomats who are trained to talk a lot but to say little). The Mishna explains that one can become a nazir with such phrases as "I will curl my hair, I will bring birds (the sacrifice associated with nezeeroot), I am like the son of Manoch". A most interesting question arises when one takes a vow to become a Nazir without realizing the full extent of the restrictions involved, or when one wants to be a partial nazir whereby they will not drink wine but want to attend funerals. Other topics include what happens if one makes aliyah while a nazir, parents taking vows of nezeeroot for their children, the punishment for violating a vow of nezeeroot, the exact definition of impurity vis a vis a nazir. 

A fascinating question arises if a kohen and a nazir are walking together and come across and abandoned body - whose immediate burial allows and obligates all to become impure and to put aside any mitzvoth one may be in the midst of performing - who should be the one to "defile" themselves.
 
Interestingly the Mishna does not discuss whether it is a good - or terrible idea - to take a vow of nezeeroot. The only allusion to what is great debate in Jewish thought is the last Mishna of the masechet which records a Taanitic debate as to whether the prophet Shmuel was a nazir. 
 
[1] When I was a student at Yeshiva University Rav Schachter in testing people for entrance to the Kollel would often ask if a woman can be a Nazir. Prospective kollel aspirants would often think long and hard trying to answer this question. Of course the answer needs little thought, being found in the verse that introduces the nazir "When either man or woman shall clearly utter a vow, the vow of a Nazirite" (Bamidbar 6:2).