134 



EXPERIMENTAL PHYSIOLOGY. 



and reservoir are firmly mounted on a stand furnished with a millimeter scale, 

 which is attached to the stand in such a way that it can be adjusted to bring its 

 zero to the surface of mercury in the reservoir, as this varies at different pressures. 

 The free end of the barometer tube is connected by rubber pressure tubing to a 

 glass T-piece (A), one limb of which is similarly connected to a stout-walled 

 (filtration) flask (F) joined to a good water pump (P). A capillary tube closed 

 by a piece of rubber tubing and a screw clip (3) also passes through the stopper 

 of the flask. 



THE DIFFERENTIAL MANOMETER. The manometer 

 shown in Fig. 36a consists of a U-tube of capillary 

 tubing furnished with 3-way stopcocks the side tubes 

 of which connect with small bottles. Suspended from 

 the stoppers of the bottles are small glass spoons. 

 The fluid in the manometer is clove oil. The mano- 

 meter is mounted on a board with a hook on its back 

 by which the board can be hung on a square glass 

 (museum) jar containing water. The bottles should be 

 immersed in the water up to the necks. 



The first step is to rinse out the tono- 

 meter with 0.9 per cent, saline and connect 

 it with the side tube of the barometer T-piece 

 A. The pump P is turned on with screw clips 

 1 and 3 closed, but screw clip 2 open and the 

 pressure lowered until the mercury stands at 

 a constant level in the barometer. Screw clip 

 4 is closed and the mercury observed, to see 

 whether there is any leak. Provided there is 

 none, clip 3 is cautiously opened and the 

 mercury allowed to fall almost to the level in the reservoir (R) ; 

 clip 2 is tightened, the tonometer, T, removed and the pump turned 

 off. Defibrinated or oxalated blood (whipped ox blood is most suit- 

 able for large classes, but in any case blood from an etherized 

 animal must not be used) is now sucked into the tonometer, by 

 placing some of the blood in a small evaporating dish, and, with 

 the rubber tube dipping into it, cautiously loosening clip 1; 3 to 4 

 c.c. of blood should be allowed to enter the tonometer. This is 

 then reattached to the T-piece A of the barometer and with clips 

 2 and 4 open (but 1 and 3 closed) the pump is turned on and the 

 mercury allowed to rise as far as it will go when clip 4 is closed . 

 and the pump turned off. Clip 3 is now cautiously opened until 



FIG. 36A. 



