The relation of hydrogen ion concentration to the action of the local anæsthetics / J.W. Trevan and E. Boock.

  • Trevan, J. W. (John William)
Date:
[1927?]
Catalogue details

Licence: In copyright

Credit: The relation of hydrogen ion concentration to the action of the local anæsthetics / J.W. Trevan and E. Boock. Source: Wellcome Collection.

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    the base [BOH]. Then if the ion could be obtained free from base, the concentration of ion necessary to produce anaesthesia would be r times the concentration of base necessary. The anaesthetic activity of a mixture of base of concentration [BOHJ and ion of concentration [BJ would be equivalent to a concentration of base of [BOH* + j. B J. Then in two solutions of the salt of equal anaesthetic activity at different pH’s x and y— [BOHJ + l [BJ = [BOHJ + } [BJ, where [BOHJ is the concentration of base at pH*, >> _BJ ” ” ion ,, pH*, „ [BOHJ ,, „ base ,, pH*,, jj _HJ ,, ,, ion ,, pHy. ■' ■ [{ [BJ - [BJ } = [BOHJ - [BOHJ, . [BJ - [BJ ' • [BOHJ - [BOHJ • In the solution just strong enough to cause anaesthesia at pH 5, there is 0'0000367 M base and 0T884 M ion present, calculated from equations 1 and 2, and the value of r obtained by substitution in equation is approximately 4000. Whereas if the concentrations are worked out for pH 7 and 8, the value of r is only 5'1, and the curve connecting log C and pH, if r had been constant, would therefore have had a pronounced convexity towards the abscissse between pH 5 and pH 8. Since it is unlikely that there would be such a large change in the value of r with alteration in pH, the conclusion seems inevitable that the ion has no anaesthetic activity. The explanation (c) of the discrepancy by the possession of anaesthetic activity by the undissociated salt is eliminated by a similar argument, which will show that this would also make the relation between log C and pH a curved and not a straight line. We are therefore left with explanation (d), namely, that the reaction to which the nerve-fibre is exposed is nearer neutrality than that of the applied solution; so that the nerve-ending will be exposed to a smaller base concentra¬ tion on the alkaline side and larger on the acid side, than that which is calculated from the observed pH and limiting concentration. That variations of reaction do take place in the corneal tissues on applica¬ tion of acid on alkaline fluids to the eye can be demonstrated in several ways: 1. If a 1% solution of neutral red is applied to the cornea, changes in colour of the stained corneal epithelium can be demonstrated when buffered solutions of various pH’s are applied to the eye. 2. The reaction of the aqueous humour in a pithed cat becomes more alkaline when alkaline buffer solution is applied to the cornea for a period of 10 minutes. 3. If a 1% solution of cocaine hydrochloride brought to a pH of 3 to 4 with HC1 is applied to the eye, as long as the instillation is continued, even for a prolonged period, no anaesthesia develops ; but within half a minute of the