In this historic image, a laboratory scientist was conducting a demonstration of a pH test on some bovine milk samples, extracted in order to study an outbreak of mastitis in a herd of cows. This photograph was taken in the Veterinary School at the University of Minnesota, October, 1934. This study focused on the causes of mastitis in cows, which was a public health concern, because mastitis can increase levels of harmful bacteria in milk supplies. This is one of a series of instructional images, used by the Minnesota Board of Health to train public health workers. The purpose of the images, and the training, was focused on the protection of Minnesota livestock, and animal husbandry.