Negative slide showing line chart demonstrating 'exhibition of all groups: tenth day classification'. Negative slide shows a line chart demonstrating 'exhibition of all groups: tenth day classification'. X axis shows time in days from 1 to 11, Y axis shows 'index of exhibition from 0.1 to 1.0'. There are four lines on the chart, identified by symbols which are labelled below. Title below image reads: 'Figure 8. Exhibition of all groups: tenth day classification. A, Hutchison's B, Perolin. [blank circle] class I cultures without nipagin; [blank square] class III cultures without nipagin; [white circle] class I cultures with nipagin; [white square] class III cultures with nipagin.' Late 19th to early 20th century