16 SCIENCE PROGRESS 



able to estimate directly— that is, the difference between the 

 chloroform vapour pressure in the inspired and in the expired 

 air. But still we can deduct that when this difference is great 

 the whole scale will be steep, and that the vapour pressure in 

 the lymph will be considerably less than that in the inspired 

 air. Early in anaesthesia we should expect, accordingly, a 

 marked difference in the chloroform content between the inspired 

 and the expired air; and this is precisely what one finds by 

 experiment to be the case (A. D. Waller and B. J. Collingwood, 

 " Estimation of Inspired and Expired Chloroform," Proceedings of 

 Physiological Society, February 25, 1905). 



There is another point which is worthy of notice — namely, 

 the ratio between the first and second step in this scale. Now, 

 so far as the writer is aware, no attempt has been made to 

 estimate the chloroform vapour pressure in the alveolar air 

 during anaesthesia ; thus one can only arrive at its value at 

 the present time by deductive methods. Oxygen fortunately 

 affords a most instructive parallel in which the alveolar tension 

 has been estimated by Haldane and Priestley. The figures 

 given by these observers show that the difference between 

 alveolar and expired air oxygen pressure is much less than that 

 between inspired and expired air oxygen pressure. Such a 

 result is only to be expected when one considers that the " dead 

 space" in breathing is estimated by these observers to be only 

 30 per cent, of the volume of tidal air. To take an example : 



Let the tidal air = 600 c.c. 



Then the "dead space" will = 200 „ 



Let the inspired air contain 2 per cent, of chloroform. 



Let the expired air contain 1 per cent, of chloroform. 



Then, as the dead space will contain 4 c.c. of chloroform, 

 the alveolar air must contain 2 c.c. of chloroform (6 — 4), and the 

 percentage of chloroform in the alveolar air must be 0*5 percent. 

 We thus arrive at the following figures : 



Inspired air. Expired air. Alveolar air. 



2 per cent. 1 per cent. o"5 per cent. 



Substituting x+y for percentage in inspired air, and x for 

 percentage in expired, we find the following result : 



Inspired air. Expired air. Alveolar air. 



x +j per cent. x per cent. x -2- per cent. 



2 



