Now another matter thrust itself upon my attention; my mouth and throat were full of saliva, and I didn't know what to do with it. At this point--and a vital one it is--my instructor had failed me. There are so many things to remember that it is surprising more is not forgotten. I became desperate. My predicament was far worse than a patient's in a dentist's chair with jaws clamped wide open and a rubber sheet jammed between his teeth. In the latter case one can signal with his hands, and indeed, under great provocation, a man has been known to kick the shins of his tormentor. But I knew that neither signalling nor kicking would now do me any good. There were questions, pressing questions, that I wished to ask; and I could not open my mouth to ask them. I could not even talk through my nose, for that was in a vise. My head now felt like a Noah's ark. It was a case of strangle or swallow. I decided that I had a choice between allowing the saliva to pour through the tube into the chemical can of the mask, or of somehow getting it down my throat. I took a deep breath, held firmly to the mouthpiece, and swallowed. Later I learned that I had done exactly the right thing. Minutes passed, and my eyes began to burn, and my goggles became blurred. I heard muffled coughing, and a sweat broke out upon me; were we to be trapped without a chance for our lives? But no orders came, and we waited on. Being in a group and in the station of a special gas sentinel, I knew that we were to depend upon this sentinel for further instructions and not to "test for gas" ourselves. Testing for gas is done by filling the lungs to their utmost capacity through the tube, releasing the nose-clamp, pulling the mask slightly away from one cheek, and sniffing. If gas is still about, the odor will be detected _unless the gas is odorless_; and the lungs, being already occupied by air, will not be affected. However, if your test has revealed the presence of gas, your mask has now become filled with the poison, and this must be got out. After readjusting the nose-clamp the lungs are emptied, and refilled through the breathing-tube; then simultaneously the mask is pulled away quickly from the cheek, and the breath instead of being exhaled through the tube is blown violently into the mask itself. By repeating this rather hazardous operation several times the mask is entirely cleared.