In order to communicate with the interior of the chamber, maintain a ventilating air-current, and provide for the passage of the current of water for the heat-absorber system and the large number of electrical connections, a number of openings through the walls of the chamber were necessary. The great importance of maintaining this chamber absolutely air-tight renders it necessary to minimize the number of these openings, to reduce their size as much as possible, and to take extra precaution in securing their closure during an experiment. The largest opening is obviously the trap-door at the top through which the subject enters, shown in dotted outline in fig. 7. While somewhat inconvenient to enter the chamber in this way, the entrance from above possesses many advantages. It is readily closed and sealed by hot wax and rarely is a leakage experienced. The trap-door is constructed on precisely the same plan as the rest of the calorimeter, having its double walls of copper and zinc, its thermal-junction system, its heating wires and connections, and its cooling pipes. When closed and sealed, and the connections made with the cooling pipes and heating wires, it presents an appearance not differing from any other portion of the calorimeter. The next largest opening is the food-aperture, which is a large sheet-copper tube, somewhat flattened, thus giving a slightly oval form, closed with a port, such as is used on vessels. The door of the port consists of a heavy brass frame with a heavy glass window and it can be closed tightly by means of a rubber gasket and two thumbscrews. On the outside is used a similar port provided with a tube somewhat larger in diameter than that connected with the inner port. The annular space between these tubes is filled with a pneumatic gasket which can be inflated and thus a tight closure may be maintained. When one door is closed and the other opened, articles can be placed in and taken out of the chamber without the passage of a material amount of air from the chamber to the room outside or into the chamber from outside.