ROUTINE OF AN EXPERIMENT WITH MAN. 101 



is sealed off between the two levels of the sulphuric acid in the two absorb- 

 ing vessels. A few seconds after the motor is stopped the valve cutting off 

 the tension-equalizer from the rest of the system is closed, the pet-cock con- 

 necting this with the petroleum manometer is opened, and oxygen is 

 admitted by short-circuiting the electrical connections at the two mercury 

 cups. This is done by the hands of the observer and must be performed 

 very gently and carefully, as otherwise oxygen will rush in so rapidly as to 

 cause excessive tension. As the bag fills with gas, the index on the petro- 

 leum manometer moves along the arc of a circle and gradually reaches the 

 desired point. At this point, the supply of oxygen is cut off, the valve con- 

 necting the tension-equalizer with the main system is opened, and simul- 

 taneously the needle-valve on the reduction-valve of the oxygen cylinder is 

 tightly closed, preliminary to weighing the cylinder. At this point the 

 motor can be started and the experiment continued. 



It is necessary, then, that the oxygen cylinder be weighed. This is done 

 after first closing the pet-cock on the end of the pipe conducting the gas 

 beneath the floor of the calorimeter room, slipping the glass joint in the 

 rubber pipe leading from the reduction valve to the pet-cock, and breaking 

 the connections between the two rubber pipes, the one from the pet-cock 

 and the other to the reduction valve, also breaking the electrical connection 

 leading to the magnet on the cylinder. The cylinder is then ready to swing 

 freely without any connections to either oxygen pipe or electrical wires. 

 It is then weighed, the loss in weight being noted by removing the brass 

 weights on the shelf attached to the counterpoise. It is important to see 

 that there is a sufficient number of brass weights always on the shelf to 

 allow for a maximum loss of weight of oxygen from the cylinder during 

 a given period. Since the cylinders contain not far from 4 to 5 kilograms 

 of oxygen, in balancing the cylinders at the start it is customary to place 

 at least 4 kilograms of brass weights on the shelf and then adjust the 

 counterpoise so as to allow for the gradual removal of these weights as the 

 oxygen is withdrawn. 



As soon after the beginning of the period as possible, the U-tubes are 

 weighed on the analytical balance, and if they have not gained too much 

 they are connected ready for the next analysis. If they have already ab- 

 sorbed too much water or carbon dioxide, they are replaced by freshly filled 

 tubes. 



Immediately at the end of the experimental period the barometer is 

 carefully set and read, and the reading is verified by another assistant. 

 Throughout the whole experiment an assistant counts the pulse of the sub- 

 ject frequently, by means of the stethoscope, and records the respiration 

 rate by noting the lesser fluctuations of the tambour pointer on the smoked 

 paper. These observations are recorded every few minutes in a book kept 

 especially for this purpose. 



