Can Bootstrap responsive cancel some style when a site viewed via mobile

Can Bootstrap responsive cancel some style when a site viewed via mobile

--------------------------------CSS---------------------
.image {
height:50px;
}
---------------------------------HTML--------------------
<div class='span6'>
<img class='image' />
</div>
<div class='span6'>
<img class='image' />
</div>
Is it possible to cancel the style when the Bootstrap's responsive works?
I need these image to be displayed without crop by CSS, assuming that the
picture's height is 400px.
Thank you