Abstract
The procedure is based upon the observation of Denigès 1 that lactic acid, in the presence of concentrated sulphuric acid, is converted into acetaldehyde, and can then be detected by certain reagents, particularly phenols and morphine alkaloids.
5 c.c. of untreated whole blood or serum is delivered directly into 15 c.c. of acidified copper sulphate solution, the flask being in the meanwhile gently shaken. It is heated 4-5 minutes on the water bath, cooled, and an excess of powdered calcium hydrate is added. It is then allowed to stand for 30 minutes and filtered. A water-clear solution is obtained which is free from sugar and other aldehyde forming substances, and which does not char appreciably during the subsequent treatment with sulphuric acid. One part of filtrate is added cautiously to 4 parts of pure concentrated sulphuric acid, the mixture being meantime shaken and cooled in a dish of ice water. It is then placed in the boiling water bath for 2 minutes and immediately cooled in ice water, after which 3 drops of 5 per cent, solution of guiacol are added. With pure lactic acid solutions a rose color is developed which remains stable and clear for some time. The maximum color is developed in the blood filtrates in about 20 minutes and it must then be read against standards prepared with known amounts of lactic acid (conveniently prepared from zinc or lithium lactate). An appreciable color is produced by 0.01-0.02 mg. of lactic acid. The colors may be compared in small flat-bottomed Nessler tubes, or the concentrated acid solutions may be compared in the Duboscq colorimeter without injury to the cups. On prolonged standing a turbidity develops in the blood filtrates which renders it impossible to read them accurately.
Get full access to this article
View all access options for this article.