NORMAL PROCESSES OF ENERGY METABOLISM 527 



of water vapor given up by D! or D 2 to the dry air passing through it may 

 be actually more than the amount of carbon dioxid absorbed, or that the 

 bottle D! or D 2 may be losing weight; on the contrary, the water vapor 

 given up is immediately absorbed by E, . and hence the algebraic sum of the 

 difference in weight of the two bottles gives the weight of the carbon dioxid 

 absorbed. Usually both bottles are weighed on a balance at the same time. 

 The loss in weight of the cylinder, L, gives the amount of oxygen absorbed 

 by the subject, corrections being made for any variation in temperature 

 and barometric pressure. Corrections for changes in composition ;of air 

 inside the chamber may be made by withdrawing samples through a by-pass 

 not shown in the figure. 



The infant is placed inside a wire crib supported at one end upon a 

 stout spiral spring, IT, and at the other end upon a knife edge, G ; this 

 mode of suspension affords a means of recording the muscular activity of 

 the infant. Alongside the spring, IT, is a pneumograph, II, the distention 

 or contraction of which compresses the air inside of the pneumograph 

 tube, thus transmitting to a delicate tambour outside a record of the light- 

 est motion of the cage. 



The respiration chamber is constructed of galvanized iron or copper, 

 and is 77 cm. long, 25 cm. deep, and 37 cm. wide. To insure temperature 

 control the whole respiration chamber is surrounded by a water jacket 

 consisting of a second shell of galvanized iron or copper with a space of 

 5 cm. between the two walls. The water jacket which is filled with water 

 to within a few centimeters of the top acts also as a seal when the cover is 

 placed upon the apparatus. In the cover are a window securely fastened 

 and an opening for the air thermometer. 



The psychrometer is essential for indicating the degree of moisture in- 

 side the respiration chamber. This is of value not only for the comfort 

 of the infant, but also for computing the amount of oxygen inside the cham- 

 ber at the end of the experimental period. Experiments carried out with a 

 very delicate instrument have shown that the depression of the wet-bulb 

 thermometer can be measured with great accuracy and the amount of water 

 vapor in the air computed with an exactness sufficient for all practical pur- 

 poses. The two thermometers are graduated to 0.1 C. but are capable 

 of being read with a lens to .02 C. It is necessary to make sure that 

 the cloth around the wet bulb thermometer is kept thoroughly drenched 

 with distilled water, also that the capillarity of the fiber is good as other- 

 wise the cloth may become partially dried and inaccurate results obtained. 

 Prior to each experiment the wet bulb is drenched by using an elongated 

 medicine dropper filled with distilled water. 



The blower, P, is connected with a leather belt to a small electric motor 

 and can be provided with a safety clutch to prevent reversing the wheel 

 through carelessness, and the drawing over of sulphuric acid from the water 

 absorbers. The safety trap, A, is an additional security against this mis- 



