ELEMENTARY EXPERIMENTAL PHYSIOLOGY 



189 



evacuated before use. In using the pump the manipulations are as 

 follow : F is placed in the position indicated by the dotted line. A is 

 raised and B is put in connection with F, and F is filled with mercury. 

 The tap on the rubber tube at the upper end of F is then closed, 

 and A lowered until F is exhausted, except for 2 or 3 c.c. of mercury 

 which are purposely left within. 



F is next 



1 2 3 



FIG. 185. The three-way tap of the mercury pump. 



The screw-clip on the lower end of F is next closed, and F is then 

 detached from the pump and weighed. A sample of blood is collected 

 in the following way : The arterial or venous cannula is connected 

 by a rubber tube to F, and the tap turned so that the cannula and 

 tube as far as the tap are filled with blood. A sufficient quantity of 

 blood is now withdrawn by turning the tap into connection with F. 

 It is now detached, and the blood is defibrinated by shaking it 

 with the mercury left within F for the purpose. F is then again 

 weighed, and the weight of the sample obtained, 

 affixed to the tube E, and E is exhausted. 

 Finally the screw clip between E and F is opened, 

 and the gases are withdrawn and collected in the 

 eudiometer. To facilitate the escape of the gases 

 F is placed in warm water and shaken. If the 

 blood froths too violently the frothing can be 

 allayed by pouring some warm water on the tube 

 E. The tap is so manipulated that the gases only, 

 and not the water which condenses in B, are driven 

 over into the eudiometer. The water is returned 

 back into F. Several exhaustions are needed to 

 extract the gases. The eudiometer tube is filled 

 with mercury and surrounded with a water jacket 

 to keep the temperature constant. The eudio 

 meter is transferred to a vessel of mercury and 



, , iiii,. Fl - 186. C. mercury 



the volume of gas read, the level of mercury vessel; t. eudiometer; 



inside and outside the eudiometer being the same. p ' plpctte> 



The temperature of the water in the jacket of the eudiometer is also 



