“Anyone who touches his bed must wash their clothes and bathe with water, and they will be unclean till evening (verse 5: וְהַנֹּגֵעַ בְּמִשְׁכָּבוֹ יְכַבֵּס בְּגָדָיו וְרָחַץ בַּמַּיִם וְטָמֵא עַד־הָעָרֶב׃). During the discussion of the zav, someone who most likely had a bacterial infection of their genitals, the torah introduces the concept of midras. In the complicated regime of tumah and tahara- purity and impurity-, certain levels of impurity impart impurity in different ways to others. A main source of tumah- or av ha tuma- imparts impurity mostly by coming in contact with another person or object thereby imparting a lower level of impurity. This gets much more complicated when dealing with dead bodies and creepy animals. For a zav or zava, midras is a unique way of imparting impurity. A midras is an object that is usually used for the purpose of someone resting or standing or riding on it. Rambam provides five examples: 1) sitting on the midras e.g., like a chair or bench, 2) lying on the midras like a rug, 3) leaning on the midras, 4) standing on the midras like a mat, 5) hanging from the midras. Once the zav or zava imparts impurity to the midras then midras object can then pass first level impurity to something else in seven ways- if the person touches the midras, carries the midras, sits on the midras, lies on the midras, leans on the midras, stands on the midras or hangs from the midras. The midras object is powerful enough to pass along tumah to someone through multiple layers. For example, if a saddle became a midras object because a zav rode on it, and then someone else placed ten layers of blankets on top of the saddle before riding it, the second rider would still contract first level tumah. The idea behind the midras is unknown. Perhaps due to the physical as well as spiritual contagious nature of the zav or zav, the Torah and subsequently the rabbis, wanted to create extra levels of protection.