358 Messrs. G. A. Buckmaster and J. A. Gardner. [Aug. 19, 



curves has convinced us that some trace of an initial danger-point is 

 rarely absent. 



Effect on the Lung-ventilation of Re-ancestlietisation of Animals by Chloroform 

 after Recovery from a Previous Ancesthetisation by this Drug when the 

 Reflexes are well marked and Voluntary Movements begin. 



In former papers we have shown that the chloroform content of the blood 

 rises in the initial stage of anaesthesia with great rapidity to a value which 

 approaches a maximum. During this period the amount of chloroform in 

 the blood appears to affect chiefly the respiratory centres, so that the 

 breathing becomes slower, and sometimes ceases altogether, and this is 

 illustrated in the experiments already described. If the animal passes this 

 stage naturally, or recovers on cessation of the anaesthetic, or is revived by 

 means of artificial respiration, then, on continuing the anaesthetic, the 

 amount of chloroform in the blood again rises quickly towards a maximum 

 value, and an equilibrium between the factors which determine the amount 

 of chloroform in the blood is established, the processes of intake and 

 elimination at the pulmonary surface going on side by side.* After the 

 animal passes this first stage of anaesthesia, or if an animal is re-chloroformed 

 after it has so far recovered from a previous anaesthetic that the reflexes have 

 become well marked, it appears to acquire a certain degree of apparent 

 tolerance to the drug, with the result that the drug has a much less effect 

 than would be the case, had not the animal been previously chloroformed. 

 After recovery from chloroform to the point mentioned, the ventilation of 

 the lung takes place at a lower level, both as regards frequency and depth of 

 respiration. If the respiration happens to be deep, the frequency is generally 

 correspondingly diminished. At this lowered level of respiration, the initial 

 effects, when chloroform is again administered, are much less marked, even 

 with very high percentages of chloroform. These points are well illustrated 

 in the following examples : — 



Example I. — The cat, from which the data of fig. 5 and Curve II were 

 constructed, one minute after cessation of respiration, exhibited asphyxial 

 convulsions, from which it recovered naturally, and, four minutes later, was 

 respiring normally and regularly. Eighteen minutes after cessation of 

 respiration, the animal had so far recovered as to make voluntary 

 movements. It was then re-chloroformed with 4-5 per cent, chloroform. 

 The frequency, amplitude, and total lung ventilation are given in Curve III. 



After 10 minutes the animal ceased to breathe for one minute, and the 

 chloroform was taken off, then a series of asphyxial gasps set in for five 

 * ' Eoy. Soc. Proc.,' 1907, B, vol. 79, pp. 255 and 580. 



