184 EXPERIMENTAL PHARMACOLOGY 



stethograph drum), and at the bottom is the base line and 

 time marker. The drum should have an approximately 

 constant slow speed. 



The arrangement of the apparatus and records is shown 

 in Fig. 175. The anesthesia should be fairly light and 

 maintained solely with ether (since morphine is injected 

 later). If the apparatus is in good condition the anesthe- 

 sia will be approximately constant. Observe the character 

 of the tracing on the drum, also Fig. 180. The thin narrow 

 curved lines in the oxygen consumption record are made 

 while the drum is standing still. This narrow line repre- 

 sents the downward movement of the lever as the pan is 

 filled with oxygen. The extent of this down stroke is op- 

 tional but should be regulated by the tension of the oxygen 

 on the bath cap. The cap should not lie filled so full as 

 to stretch it, as this would cause too great a mechanical 

 obstruction to the breathing of the animal'. This must be 

 carefully avoided. When the pan is filled sufficiently with 

 oxygen the writing lever will have descended to a certain 

 level on the drum. This level marks what may be termed 

 the lower base line for the oxygen record. In filling the 

 pan with oxygen at all later times see to it that the lever 

 again descends to this same level as nearly as you can de- 

 termine. This is done by watching the lever go down as 

 oxygen is run in very cautiously. Conversely the highest 

 point in the oxygen record may be called the upper base 

 line for this record. If while the drum is stopped the lever 

 be run down to the lower base line by adding oxygen to the 

 pan, then just as the lever reaches the base line the injec- 

 tion of oxygen is stopped and the drum is started. (It is 

 desirable that the drum start quickly and soon reach the 

 maximum for that rate of speed.) As the drum runs the 

 lever moves up and down a short distance rapidly at each 

 inspiration and expiration. We are not much concerned 

 now with these short, rapid movements as they correspond 

 fairly closely with the respiration tracing from the stetho- 



