In this chamber it is impossible to weigh the bed and clothing, and hence this calorimeter can not be used for the accurate determination of the moisture vaporized from the lungs and skin of the subject, since here (as in almost every form of respiration chamber) it is absolutely impossible to distinguish between the amount of water vaporized from bed-clothing and that vaporized from the lungs and skin of the subject. With the chair calorimeter, the weighing arrangements make it possible to weigh the chair, clothing, etc., and thus apportion the total water vaporized between losses from the chair, furniture, and body of the man. In view of the fact that the water vaporized from the skin and lungs could not be determined, the whole interior of the chamber of the bed calorimeter has been coated with a white enamel paint, which gives it a bright appearance and makes it much more attractive to new patients. An incandescent light placed above the head at the front illuminates the chamber very well, and as a matter of fact the food-aperture is so placed that one can lie on the cot and actually look outdoors through one of the laboratory windows. [Illustration: FIG. 26.--Cross-section of bed calorimeter, showing part of steel construction, also copper and zinc walls, food-aperture, and wall and air-resistance thermometers. Cross-section of opening, cross-section of panels of insulating asbestos, and supports of calorimeter itself are also indicated.] Special precaution was taken with this calorimeter to make it as comfortable and as attractive as possible to new and possibly apprehensive patients. The painting of the walls unquestionably results in a condensation of more or less moisture, for the paint certainly absorbs more moisture than does the metallic surface of the copper. The chief value of the determination of the water vaporized inside of the chamber during an experiment lies, however, not in a study of the vaporization of water as such, but in the fact that a certain amount of heat is required to vaporize the water and obviously an accurate measure of the heat production must involve a measure of the amount of water vaporized. So far as the measurement of heat is concerned, it is immaterial whether the water is vaporized from the lungs or skin of the subject or the clothing, bedding, or walls of the chamber; since for every gram of water vaporized inside of the chamber, from whatever source, 0.586 calorie of heat must have been absorbed.