The side of the hill facing the German trenches was absolutely deserted, but the opposite slope the ambulanciers found densely crowded with poilus. And these soldiers of the twentieth century had virtually become modern cave men; for, imitating the example of their primitive ancestors, they had burrowed into the earth and made for themselves habitations. There were hundreds and hundreds of dugouts in the immediate vicinity, all so skilfully concealed or disguised by various devices that a German airman flying directly overhead would in all probability not have discovered their presence. A long time passed before Chase felt in any mood to join in the conversation, and then, thoroughly disgusted at having allowed his feelings to be so plainly seen, he became more than usually sullen. Suddenly the ambulanciers discovered that there were other sounds in the air besides the distant booming of cannon and the occasional explosion of a shell. "Music, as I live!" cried Don Hale. "Where in the world is that coming from?" He addressed the artillery lieutenant. "The theatrical performance has just started," answered the officer, with a smile. "Perhaps Messieurs would like to witness the comedy? Plenty of bomb-proof shelters close by," he added, pleasantly. "Should we like to see it? Yes, indeed," cried the aviator's son, enthusiastically. "And thus the scene shifts from near-tragedy to comedy!" laughed Dunstan. "Coming, Chase?" The latter had been showing no inclination to budge from his position, but in answer to the question he gave a gruff assent, then slowly rose to his feet, and Don, standing near by, heard him mutter: "Awful, awful! I can scarcely believe I'm alive." As the three Americans followed their soldier-guide along the foot-path, which wound its way in a serpentine direction through the forest, they were greeted everywhere with cordial salutations. The way led past an amazing number of subterranean retreats, representing such a vast amount of time and labor that Dunstan could not help remarking thoughtfully: "Too bad that so much energy had to be put into work of such a character!" "I guess that thought was in the mind of every one who helped to dig," growled Chase.