124 VITALITY AND EFFICIENCY WITH RESTRICTED DIET. 



experiments with the series of subjects, this blower was kept in opera- 

 tion to sweep out the air in both skirt and cover. Two windows on 

 opposite sides of the room gave a rapid means of ventilation. 



TENSION EQUALIZERS. 



On the left side of the skirt near the front was soldered a 2.5 cm. 

 coupling, to which were connected two spirometers, M and M', with a 

 capacity of 7.2 liters each. These spirometers were connected in series 

 by a 3-way valve and were designed to allow for any change in volume 

 of the chamber due to barometric or temperature conditions. Only 

 one spirometer was regularly used, the second being kept in reserve for 

 any sudden and unexpected changes which might occur. In practice 

 it was found that any ordinary changes in volume could be controlled 

 by changing the temperature of the room; at no time was it necessary to 

 use the second spirometer. 



The position of the spirometer was read on a millimeter scale at the 

 beginning and end of each period under a uniform pressure as indicated 

 by a Sonden oil manometer attached to the skirt of the chamber. The 

 spirometer had been previously cahbrated and each change of 1 nam. 

 in the level of the spirometer bell was equivalent to a change in volume 

 of 21.5 c.c. 



RESISTANCE THERMOMETERS. 



The temperature of the chamber was measured by means of six 

 resistance thermometers, made of silk-covered No. 33 copper wire 

 which was wound on wooden frames 4 by 15 cm. These were fastened 

 to the walls of the chamber by studs 35 mm. long. One thermometer, 

 iV\ was placed near the top, another, A^, near the bottom of the cover, 

 one each (A^^ and N^) was placed at the front and back of the skirt, 

 respectively, about 20 cm. above the belt of the treadmill, while the 

 remaining two (only one, N\ is shown in the figure) were placed 

 below the belt near the rear and front pulleys of the mill. The six 

 thermometers were connected in series and had a total resistance of 

 98 ohms. The leads left the chamber by means of brass rods, which 

 passed through a hard-rubber plug, P, set into the front of the cover 

 by means of gaskets and bushings. From this plug double leads of 

 No. 14 copper wire carried the current to a galvanometer and Wheat- 

 stone bridge in the adjoining gas-analysis room. Readings of 0.003 

 ohm were mfide, corresponding to a temperature difference of 0.01° C. 



BAROMETER. 



The barometer was a standard observatory pattern graduated so 

 that 0.05 mm. could be read by means of the vernier. 



GAS-ANALYSIS APPARATUS. 



The carbon dioxide in the chamber was determined in duplicate by 

 means of two small Haldane gas-analysis apparatus.^ These instru- 



^ Haldane, Methods of air analysis, 1912, p. 62. 



