Unknown. 1926. “A typical swine herd with with roundworm (Ascaris suum) resulting from indiscriminate breeding and little attention to sanitation. Note improved farrowing shelter in the background. Photograph used as Figure 2 in U.S. Department of Agriculture Technical Bulletin 374, 1933..” Special Collections, USDA National Agricultural Library. Accessed February 5, 2023, https://www.nal.usda.gov/exhibits/speccoll/items/show/8068.