פירוש על ידים 4:1

בו ביום – This refers to the chapter above regarding the words of Rabbi Shimon ben Azzai, that speaks of the day when they appointed Rabbi Eleazar ben Azariah in the Academy [as the Nasi/president]. And every place where it states, "בו ביום" /on that day, in the Mishnah, it is regarding that day which is spoken of.

Introduction Yesterday's mishnah ended with the statement that the sages voted on whether to include Kohelet and Shir Hashirim in the canon. This is taken as referring to a vote that occurred in the academy in Yavneh on a momentous day in history. Today's mishnah continues with other momentous issues they voted on on that famous day.

נמנו (they were counted – i.e., the votes were taken [and they decided]) – they stood for the count, to whom the number of those defile and the number of those who purify, and they decided the law according to the majority.

On that day the votes were counted and they decided that a footbath holding from two logs to nine kavs which was cracked could contract midras uncleanness. You just have to love this transition. In yesterday's mishnah we hear of a vote over whether a book should be part of the Bible. It's hard to think of a more fateful issue than this if the vote had turned the other way, these two books might have been lost, or at least cut out of the Jewish tradition. The second issue was over the purity of a cracked footbath and whether it can still receive midras uncleanness. Since it can no longer hold liquids, it doesn't count as a vessel for bathing. But since people could still sit in it, it is still susceptible to "midras" uncleanness, the kind of impurity that is given to items that are meant to be sat or laid upon.

עריבת הרגלים – tub made for washing the feet.

Because Rabbi Akiva said a footbath [must be considered] according to its designation. Rabbi Akiva holds that anything that is called "a footbath," even if it can hold more than nine kavs, is still susceptible to midras impurity.

שנסדקה –[which was cracked] near its bottom, and it doesn’t hold water in order to wash his one foot.

טמאה מדרס – for a tub made for a foot-bath prior its becoming cracked also was customary to sit in it, and it served [as a place] to sit while working.

שר' עקיבא – he would dispute and saw that the tub for a foot-bath is like its name (i.e., for washing the feet only, and not for sitting), that is, that like its name, so it is, that there is no מדרס/Levitical uncleanness arising from someone with gonorrhea having immediate contact through treading or leaning upon it. But the Halakha is not according to Rabbi Akiva.