CHLOROFORM A POISON 17 



Thus the difference in chloroform percentage between alveolar 

 and expired air is only half the difference between the expired 

 and the inspired air. This ratio is represented in the diagram 

 given above. 



It has already been suggested that the steepness of the first 

 step in the scale gives an indication of the vapour pressure of 

 chloroform in the lymph. This fact is well illustrated by the 

 two following experiments, the first of which is taken from a 

 table in the paper already quoted by Dr. Waller and the present 

 writer on the estimation of chloroform in inspired and expired 

 air, the second of which was performed by the author at a later 

 date : 



Percentage of CHC1 3 inspired. Percentage of CHC1 3 expired. 

 Dog . . 3 "3 per cent. 1*5 per cent. 



Cat . . 1-3 „ i'2 



Firstly, we can deduct from these figures that the descending 

 scale of vapour pressures was much steeper in the dog than in 

 the cat. Secondly, we can deduct that the chloroform percentage 

 in the alveolar air of the dog was approximately o'6 per cent., 

 and in the cat approximately ri5 per cent. We therefore con- 

 clude that'the chloroform vapour pressure in the lymph of the 

 dog was considerably lower than that in the lymph of the cat. 

 Our conclusion is in accordance with the facts of the case ; for 

 the dog was in a condition of light anaesthesia, and the cat in a 

 condition of deep anaesthesia. 



We will now consider what factors influence the first step 

 in the scale — namely, the difference between the percentage of 

 chloroform in the inspired and the expired air. There are two 

 main factors with which we must deal : 



(1) The rate of absorption of chloroform by the blood. 



(2) The frequency and the depth of the respirations. 



To discuss the first of these two factors. The rate of absorp- 

 tion of chloroform is again under two influences : (a) the 

 difference of vapour pressure of the anaesthetic in the blood and 

 in the alveolar air ; and (b) the rate of blood stream through the 

 lungs. 



Early in anaesthesia, when the vapour pressure in the blood is 

 low, the rate of absorption will be rapid, and, as a consequence, if 

 the percentage in the inspired air be kept at a constant value, the 

 difference of chloroform concentration between the inspired and 



2 



