PRELIMINARY OPERATIONS 97 



pressure in the manometer until the manometer pointer 

 writes about one and one-half inches above the base line. 

 Do not raise this pressure too high. Wliy? See that both 

 clips are tightly closed and then remove the bull-clog; from 

 the artery. The pressure in the manometer should rise 

 sufficiently to lift the writing point about three-fourths or 

 one inch higher than it was. 



The pressure bottle should be suspended from a pulley 

 at the ceiling and the bottle should be kept about four or 

 five feet above the table. Some workers put the pressure 

 bottle on the table and use compressed air to force the 

 fluid out. The writer advises that this method be avoided 

 at least in student work, for all the space on the table top 

 is needed for other apparatus. Furthermore, it sometimes 

 happens that students do not properly close the clip at the 

 top of the manometer and then the dog may soon bleed 

 to death by forcing blood out into the tubes and pressure 

 bottle, while at the same time citrate solution rather quickly 

 passes down into the carotid artery. This solution is very 

 poisonous and soon kills the heart. If the bottle is sus- 

 pended above the table the instructor can quickly see if any 

 blood is backing up into the bottle. In addition it is much 

 easier for the instructor to see at a glance just how much 

 citrate solution each group of students has ahead for the 

 experiment. 



(e) Recording Respiration. Near the middle of the 

 thorax pass the long string of the stethograph drum under 

 the dog (use the hook of an aneurism needle to reach un- 

 der the animal) and bring it up on the opposite side. Ad- 

 just the two strings of the stethograph with a moderate 

 tension and damp them together trith a hemostat or bull- 

 dog. If too little movement is thus secured for the stetho- 

 graph membranes place fairly large wads of cotton under 

 the strings on either side of the chest. Now connect a 

 rubber tube (which carries near the middle a T-tube with 



