ArtTIFICIAL TtESn RATION. 2 60 



into the trachea, the ends of the ligature may be fastened round 

 the upright bend of the knee, to ensure that it do not slip out. 

 The bellows may be simply held in the hand, or fastened to the 

 under side of a table by means of a piece of board screwed to 

 its upper side and larger than the bellows itself, so that there is 

 a rim of board all round. A few screws passed through this 

 projecting rim into the under side of the table hold the bellows 

 fast. A small pulley (one used for window-blinds will do) is 

 then screwed into the under side of the table, and a cord passed 

 over it. One end of the cord is fastened to a piece of board a 

 foot and a half or two feet long, which serves as a treadle ; and 

 the other end to the under board of the bellows, so that it may 

 be drawn up when the treadle is pressed down by the foot. A 

 weight must be attached to the under board of the bellows, in 

 order to draw it down again after it has been raised. The 

 respiration is kept regular by depressing the treadle in accord- 

 ance with the beat of a metronome set to beat the proper 

 number in a minute. 



The apparatus may be rendered more complete by the intro- 

 duction between the bellows and trachea of a valve which will 

 allow the air to pass readily towards the trachea, but hinder its 

 return. Such a valve may be readily made by passing two 

 pieces of glass tubing through the cork of a wide-mouthed 

 bottle, and partially filling it with mercury or water. The tube 

 nearest the bellows must descend nearly to the bottom of the 

 bottle, while the other just passes through the cork. The air 

 from the bellow^s passes easily through the mercury or water in; 

 Y/hich the end of one tube dips ; but any attempt to return 

 simply raises the mercury in the tube. If water be used, the 

 tube must be longer, so that it may contain a column of water 

 sufficiently high to afford the necessary resistance to the return 

 of the air. This sort of valve is termed Mltller's valve. 

 (Fig. 130, V.) 



Artificial Respiration in the Frog. — Although the frog can 

 live perfectly well for some time without breatliing, it may be 

 desirable in some experiments to employ artificial respiration. 

 A cannula for this purpose is best made by heating the end of 

 a glass tube about one-eighth of an inch in diameter (more or 



