The pulmotor _makes_ the patient breathe--because it carries on the function for him artificially. "In Chicago this winter," said the boy's friend, "there were several cases where the pulmotor brought back to life people who apparently were dead, from asphyxiation, or gas poisoning. The machine is most successful where breathing has stopped through some unnatural interference, and the rest of the organs are physically intact, but of course it can be used in all surgical cases just as the ordinary oxygen tank is used. "One case, and probably the one about which your father was reading," continued the boy's friend, "was that of a family of three, father, mother and little girl, who were asphyxiated, and were apparently dead. The pulmotor pumped pure oxygen into their lungs until they began to breathe naturally again." When the pulmotor is unpacked from its little wooden box, about the size of a suitcase, it looks like a confusion of rubber tubes and bags. The oxygen is contained in the tank under high pressure, and this pressure also furnishes the power to keep up the artificial breathing. [Illustration: THE PULMOTOR A--Oxygen tank. B--Reducing valve. C--Inspirator. D-E--Inlet and outlet of controlling valve. F--Operating bellows. G--Dashpot bellows. H--Face cap.] The oxygen flows from the tank through a reducing valve, which cuts down the pressure, and into a controlling valve whence it flows by a rubber tube to the face cap which fits tightly over the patient's nose and mouth. The patient's tongue is kept from sliding back into his throat by a pair of forceps placed for the purpose. Thus, the oxygen is forced into the lungs by the pressure, but when it reaches a certain degree, about what it would be in normal breathing, a bellows connected with the controlling valve is pressed, and the pressure is turned to suction so that the oxygen that has been forced into the lungs is brought out, through the outlet, causing the poisonous gases to be expelled from the lungs. After the exhalation is complete the controlling valve works again and another blast of pure oxygen is sent into the lungs, only to be withdrawn at the proper moment. This is kept up until the patient's breathing is normal. We will leave the scientist and his young friend here, for already we have spent more time in following their journeys and talks than we set out to do. We have not touched upon every invention of the last ten years or so, nor every important development, by a long ways, but we have gone far enough to get a pretty fair idea as to the trend of modern thought in inventive research.