132 EXPERIMENTAL PHARMACOLOGY 



connects with the main air way and when in use the mer- 

 cury manometer should record a pressure of about twenty 

 millimeters. 



For an average sized dog the catheter may have an out- 

 side diameter of about three-sixteenths or one-fourth inch. 

 The catheter is slipped into the trachea down to its bifur- 

 cation and then withdrawn a little. The animal should be 

 etherized in the usual manner and then the catheter may 

 be introduced through the larynx or through the tracheal 

 cannula. The air and ether vapor blown in through the 

 catheter escapes again from the lungs between the outer 

 wall of the catheter and the inner Avail of the trachea. 

 As a rule, the dog will keep up shallow respiratory move- 

 ments while the anesthesia is carried on by this method. 

 Would it be advisable to turn the air current off for a 

 few seconds at intervals of one or two minutes'? It is ad- 

 visable for the student to practice for some time with this 

 method before attempting severe operations while using 

 it. Meltzer, Auer and their associates at the Rockefel- 

 ler Institute have extensively used and developed this 

 method, while from the University of Minnesota Hirsch- 

 felder has reported excellent results with it in ordinary 

 student experiments. Can you repeat these results ? Could 

 this method be used when the chest is opened? What pre- 

 cautions would you then take ? Could you use the method to 

 record changes in the volume of the lungs (see Figs. 187 

 and 257, also consult Experiments XXIX and LXX). 



What are the advantages of this method ? What are 

 the disadvantages I This method may be used in some of 

 the later experiments. It is often very convenient for 

 maintaining a regular anesthesia. 



This method has been much used for intrathoracic sur- 

 gery, etc., and several different forms of apparatus for 

 carrying on intratracheal insufflation have been devised 

 and used. It is very desirable for the student to become 

 familiar with the principles involved, and if possible, to 

 have some experience in using the method. 



