NITROUS OXIDE,, CARBON DIOXIDE, OXYGEN 113 



nence, and the left pulmonary artery can be seen passing 

 out into the base of the lung. Place an aneurism needle 

 beneath the artery, raise it up and clear a section of the 

 artery about three-fourths of an inch long with the probe. 

 Could you put a cannula into this artery and record the 

 pulmonary blood-pressure! The heart will probably have 

 ceased beating by this time. If it has not, stop the respira- 

 tion and let the animal die. // time permits it will be very 

 instructive to try to revive the heart by massage and by 

 injecting adrenaline. Keep up the artificial respiration 

 during these efforts. 



EXPERIMENT VI. 



Nitrous Oxide, Carbon Dioxide, Oxygen. (Frog: Central 



Nervous System.) 



1 . Place a frog in a one pint milk bottle as shown in Fig. 

 109. Arrange a nitrous oxide tank (and an oxygen tank 

 also if the laboratory can afford one if not omit the oxy- 

 gen) as shown in the illustration. The apparatus shown 

 in Fig. 110 may also be used if a nitrous oxide tank is not 

 available. Observe (and count) the rate of the frog's res- 

 piration, lymph heart beats and heart beats. Note the 

 size of the pupils, position which the frog assumes, etc. 

 Now open the N 2 tank a little and run into the bottle a 

 very small amount of the gas. Make a note of the time 

 of day. The outlet must be opened as the gas is run in, 

 for these taiiks may have 1000 pounds or more pressure 

 to the square inch and would quickly burst the bottle or 

 blow out the cork. AVatch the frog carefully as it begins 

 to breathe the gas. Does it show any signs of suffocation? 

 There was already sufficient oxygen in the bottle to run 

 the frog some time. Gradually run in more N 2 and watch 

 carefully for the first symptoms shown by the frog. As 

 the atmosphere in the bottle becomes more and more filled 



