Variable resistor and thermistors?

[CAH]

If your doing an experiment to test how the temperature affects a thermistor (increase temp measure v and I...) why do you need a variable resistor in your circuit? Or if you don't NEED one what beneficial use may it pose anyway?
Is it something to do with the current?

Thanks

 

[nasu]

It may be used to limit the current to a desired value. It can be also used to measure the current, by measuring the voltage across the resistor and knowing the value of its resistance.
If the current through the thermistor is too high, it will heat up and as its resistance decreases with temperature the current will keep increasing and so on.