50 GASEOUS METABOLISM OF INFANTS. 



the apparatus for measuring minute quantities of carbon dioxide and 

 oxygen. 



Method of computing the carbon-dioxide production. — In these alcohol 

 check experiments, the carbon-dioxide production is found by weighing 

 the soda-lime container with its accompanying Williams bottle, the 

 increase in weight giving the amount of carbon dioxide produced 

 during the period, assuming no change in the amount of carbon dioxide 

 residual in the chamber. If extreme accuracy is desired, determina- 

 tions of the residual amount of this gas are made as outlined above and 

 any variations corrected for. 



Method of computing the oxygen consumption. — The computation of 

 the oxygen consumption is much more elaborate than that of the 

 carbon-dioxide production, for while a rough measurement of the total 

 oxygen consumption can readily be obtained by noting the loss in 

 weight of the cylinder of gas or by reading directly the volume of gas 

 passing through the Bohr meter, there are nevertheless a number of 

 factors which affect these determinations, all of which must be taken 

 into consideration. For example, the spirometer bell is at a certain 

 height at the beginning of an experiment; if at the end this bell is 

 either above or below this point, a correction therefor must be applied. 

 If above, an excessive amount of oxygen has been added, and if below, 

 the amount of oxygen is deficient. As each millimeter difference in 

 the height of the spirometer bell corresponds to 23 c.c. of gas, the com- 

 putation is very simple. On the other hand, if there is an increase in 

 the temperature inside the chamber, the air expands and even if the 

 spirometer bell is in the same position at the end of the period as at the 

 beginning, less oxygen has evidently been introduced than if the tem- 

 perature had remained constant. Conversely, if the temperature has 

 fallen, more oxygen has been introduced. Similarly, if the barometric 

 pressure has altered materially, it has likewise affected the introduction 

 of the oxygen. For an exact computation of the amount of oxygen 

 consumed by the subject, therefore, not only is it necessary to know 

 the amount introduced from the weighed cylinder or through the Bohr 

 meter, making due corrections on the readings of the gas meter for 

 the factors of temperature and pressure and the mechanical factor of 

 the meter itself, but likewise a correction for the alterations in the 

 total volume of air inside the ventilating air system should also be 

 made, since any alteration of the volume of the air inside the system 

 represents a corresponding error in the oxygen introduced. For this 

 purpose, it is necessary to note, first, the volume of air inside the 

 chamber, which is roughly found by a simple computation; second, 

 the temperature of the air in the chamber as shown by the readings of 

 the two thermometers; third, the barometric pressure; fourth, the 

 degree of humidity as obtained from the wet- and dry-bulb psychrometer, 

 since the water-vapor in the chamber may also vary ; and fifth, in exceed- 



