In order that these soldiers might be properly taught the necessity of having their masks adjusted, the army officers made use of this tear-gas trench where fumes that would irritate but not permanently injure the eyes were used.
The soldier nearest to you is testing his mask to see if it is tight all about his face. With his hand he has removed the piece of rubber from his mouth and is exhaling his breath inside the mask. The mask, you can see, is inflated, proof that the edges are tight. On the mask of the third soldier you can plainly see the circular spring just below the eye pieces that is used to adjust and hold the nose grip in place to prevent breath entering the lungs except through the mouth.
All of these men have their masks at the "alert," that is, strapped high on their chests with the lower part firmly tied around their backs. You will notice too that the flaps of the case fold in toward the body, to lessen the possibility of water, dampness and dirt getting into the mask.
When these masks are adjusted the chin is inserted first and then the rest of the mask drawn over the face, being held in position by that rubber band which you can see passed over the top of the head and two rubber bands that pass around the head.