The experiment design was developed to measure the snail behavior to smell. The issue of calibration was discussed, how do we know what we are measuring is correct? for this we need calibration. If we use water on both the sides snail will move randomly, and when we keep a for example H2S at one side, the snail will go away from it. And if we keep one drop of cucumber the snail will move more times towards cucumber as against water. This happens because all smells diffuse with a concentration gradient. We discussed where the concentration will be more and where it will be less? The concentration will be more near the drop of cucumber but it will be less as we go away from the drop of cucumber.
@vaishnavi had asked why do we need to keep water and check response of snail towards water? This helps us understand how water can help us to know what is the normal response without any attractant and find out which chemical is attractant.
The experiment helps us to understand instrumentation involved in devising snail olfactometer.