564 SCIENCE PROGRESS 



All these five considerations negative the administration of a 

 high initial percentage of chloroform. But on the other hand 

 there is the factor of 



VI. Time. The relation of the time taken to produce 

 surgical anaesthesia and the percentage in the inspired air is 

 a very curious one, and deserves further study than has been 

 hitherto accorded to the subject. Neglecting for the moment 

 individual variations, percentages below 2 per cent, only induce 

 anaesthesia in the human subject if a quite unreasonable time is 

 taken in the process; in round numbers twenty minutes to three- 

 quarters of an hour may be required. This time serves no good 

 purpose — in fact, certain observations now in progress appear to 

 indicate that this delay is directly injurious. As far as our 

 present knowledge goes, anaesthesia is best accomplished 

 between the limits of seven and ten minutes, so that the per- 

 centage to be taken should be such as will lead to this result. 



It was found on actual trial that if the percentage was made 

 to have the same value as the time (up to two minutes) the 

 result was very satisfactory. In other words, at the half- 

 minute '5 per cent, was administered, at one minute 1 per 

 cent., at a minute and a half 1*5 per cent., and so on. After 

 two minutes the rise was made more gradually ; in an average 

 case 2\ per cent, was reached in three minutes, and, if necessary, 

 3 per cent, in four minutes. 



No fault could be found with the result of this routine. It is 

 very comfortable for the patient, anaesthesia is very gradual, and 

 there is a marked lessening of the so-called stage of excitement 

 often seen with the open method. But the words " if necessary " 

 indicate another difficulty, which from this point onwards has 

 always to be borne in mind, and that is the state of the patient. 

 It is not possible to blindly administer any percentage without 

 the most careful observation of the result, and, although we can 

 now go so far as to say that in an average case such and such 

 percentage will probably do such and such things, yet the 

 anaesthetist must always be on his guard for the individual 

 variations of each patient which play such an important part in 

 the human subject. 



The reader will now be in a position to understand how 

 a "chloroform curve" is constructed. Time in minutes is 

 plotted along the abscissa, percentages of chloroform on the 

 ordinates, and from such a diagram it is possible to see at 



