2 o SCIENCE PROGRESS 



reaches the left auricle to contain an increased concentration 

 of anaesthetic, and this will occur without any rise of per- 

 centage of anaesthetic in alveolar air, and, accordingly, cannot 

 be guarded against by maintaining the chloroform in the 

 inspired air at a constant level. It thus seems certain that 

 weakening of the heart is the first link in a vicious circle, for 

 the weaker the heart the stronger the concentration of chloro- 

 form which it will receive. Many observers have shown 

 that chloroform has a directly toxic influence on the heart ; 

 amongst them may be mentioned Embley, Tunnicliffe, Ronen- 

 heim, Schafer, and Scharlieb. Accordingly there can be little 

 doubt that the matter discussed above is one well worthy of 

 attention. 



We will now consider the second factor which influences 

 the differences between the percentage of chloroform in the 

 inspired and in the expired air — namely, the frequency and the 

 depth of respirations. It is sufficiently obvious that increased 

 frequency of respirations will raise the percentage of chloro- 

 form in the expired air, and so in the alveolar air, more rapidly 

 than diminished frequency. As to the depth of respiration, 

 the deeper the breathing the more rapidly will the concentration 

 in the expired air, and so in the alveolar air, rise. In both 

 the above cases it is premised that the percentage of vapour 

 in the inspired air is kept constant. From such considerations 

 it has been argued that it is actually an advantage to give 

 a higher concentration of vapour when the breathing is 

 shallow ; in addition, methods of administration which have a 

 tendency to deliver a higher percentage when the breathing 

 becomes more shallow have been defended as possessing an 

 error in the right direction. The following table throws some 

 light on this question. The data on which it is constructed 

 are given below : 



(i) Residual + supplemental air == 2,000 c.c. 



(2) Percentage of chloroform in alveolar air = 1*3 per cent. 



(3) No absorption of anaesthetic taking place. This is 

 merely to simplify the issue, for absorption would not alter 

 the main result, but would only diminish the rate of increase 

 of alveolar concentration. 



(4) To simplify the calculation complete mixture is supposed 

 to take place between the inspired and the alveolar air. 

 Corrections for "dead space" are accordingly not made. 



