$66 SCIENCE PROGRESS 



-nerely because the same phenomena are repeated time after 

 time. And yet it is plain that the curves from these forty 

 average cases deserve quite as careful study as the ten excep- 

 tional cases, if only from their greater number. All these 



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8 10 13 14 IS IB 20 22 24 26 28 30 33 34 36 38 40 42 44 46 48 50 52 54 56 58 60 I 



Fig. 2. — Typical case. 



curves show the same gradual rise, the break, and the gradual 

 fall, the latter varying from time to time according to the 

 necessities of the operation. Accordingly, the comparison of 

 the curves after the break is not easy ; but in the stage of 

 induction the same objections do not apply, so that this gap 

 forms a convenient and not very inaccurate landmark. 



It might be supposed that it would be possible to express 

 numerically from the curves the dose of chloroform that each 

 patient has had to produce anaesthesia, taking the break as 

 the end point. But the data are in reality insufficient — the 

 dose that each person actually gets is not measured by the 

 percentage in the inspired air, but by the difference between 

 this percentage and that present in the expired air. This 

 latter has not been measured in the present series of obser- 

 vations, and as it is plain from the experiments of Vernon- 

 Harcourt (4 d) and Brodie and Widdows {I.e.) that this varies 

 from time to time, it is not possible to make a general correction. 

 In addition, there is some evidence to show that, even if two 

 patients retained the same quantity of chloroform, it would not 

 necessarily produce the same result, so that this problem must 

 be left to a future occasion. All that can be said at present is 

 that the forty average cases required about the same percentage 

 from the machine, and of the ten exceptional cases some required 

 more and some less. 1 



1 Dr. Levy has published (5 e) a very interesting series of cases anaesthetised 

 with exactly 2 per cent, of vapour. The time taken to induce anaesthesia varied 

 between six minutes and over twenty minutes, showing clearly the amount of 



