"The trouble seemed to come from a cloud of some dense heavy gas which rolled in from the marsh. On the advice of Major Martin, every door and window in the post was kept closed until morning. The gas never reached the upper part of the post but it reached the stables. Eleven horses and mules are dead and all of the rest are stricken. The stable detachment either failed to close their barracks tightly or else the gas went in through cracks for seven out of the nine are here in the hospital, although none of them are very seriously ill. As soon as the sun came up, the gas seemed to disappear." "Let me see the men who are sick." Captain Murdock led the way into the ward. Dr. Bird went from man to man, examining charts and asking questions of the nurses and medical corps men on duty. When he had gone the rounds of the ward he entered the morgue and carefully examined the bodies of the men who lay there. "Have you performed any autopsies?" he asked. "Not yet." "Have you the authority?" "On the approval of the commanding officer." "Please secure that approval at once. Have all lights taken out of the operating room and the windows shaded. I want to work under red light. We must examine the lungs of these men at once. With all due respect to your medical knowledge, Captain, I am not convinced that these men died of pneumonia." "Neither am I, Doctor, but that is the best guess I could make. I'll have things fixed up for you right away." * * * * * Dr. Bird stepped to the telephone and called the laboratory. When, in half an hour, Captain Murdock announced that he was ready to proceed, Davis had arrived with an ultra-microscope and other apparatus which the doctor had telephoned for. "Did you arrange about the horses, Davis?" asked Dr. Bird. "Yes, sir. They will be up here as soon as the trucks can bring them." "Good enough. We'll start operating." An hour later, Dr. Bird straightened up and faced the puzzled medical officer. "Captain," he said, "your diagnosis is faulty. With one possible exception, the lungs of these men are free from pneumonicocci. On the other hand there is a peculiar aspect of the tissues as though a very powerful antiseptic solution had been applied to them." "Hardly an antiseptic, Doctor; wouldn't you say, rather, a cauterizing agent." Dr. Bird bent again over the ultra-microscope. "Are you familiar with the work done by Bancroft and Richter at Cornell University last November and December?" he asked. "No, I can't say that I am."