• Rats 

        Contributor:Colorado Agricultural College
        Date:1930-03-26
        One young woman measures the length of a mouse, while another young woman weighs a mouse.
      • Rats 

        Contributor:Colorado Agricultural College
        Date:1934-05-22
        A white rat, on the left, stands in front of a sign stating "with milk". A white rat, on the right, stands in front of a sign stating "without milk".
      • Rats 

        Contributor:Colorado Agricultural College
        Date:1934-05-22
        A white rat, on the left, stands in front of a sign stating "with milk". A white rat, on the right, stands in front of a sign stating "without milk".
      • Rats 

        Contributor:Colorado State College of Agriculture and Mechanic Arts
        Date:1935-10-30
        A large, white rat, being held in place by its tail, is standing on its hind legs, while a small, white rat is looking at it from the left.