Effect of exposure of excessive FGF-10 on matrigel cultured developing chicken lung. Figure 34 shows normal (control) development of the primary bronchus (PB), the secondary bronchi (SB), and the epithelium lining the airways at day four of embryonic development (arrows). MC, mesenchymal cells. Figures 35 and 36: When exposed to high concentration of exogenous FGF-10 (dissolved in matrigel) at day the fourth day of embryonic life, the primary bronchi (PB) and the secondary bronchi (SB) are aberrantly distended (asterisks) and the epithelium lining the airways is unspecified. Figure 37: A toluidine blue-stained section of a matrigel cultured lung at the fourth day of development showing an FGF-10 soaked bead (Bd) which was placed close to the developing lung (the matrigel also had high concentration of dissolved exogenous FGF-10). The secondary bronchi (SB) were bloated (asterisks) but the epithelium which lines the airways (arrows) was well-defined, particularly that associated with the primary bronchus (PB). MC, mesenchymal cells; asterisks, abnormally swollen distal parts of the secondary bronchi; dashed circle, mesenchymal cell proliferation in the area between the FGF-10 bead and the airway epithelium. Scale bars: 100 μm. From unpublished work by JN Maina and B Kramer.