Xvi. Estimation of Sugar in the Blood

FOR some years past much attention has been directed to the determination of carbohydrate tolerance by observing the variations that occur in the sugarcontent of the blood after the ingestion of a known amount of sugar. The value of this method is now universally recognised. It is not intended in this paper to treat the subject in a general way, but merely to consider the actual estimation of sugar as required for the above purpose. The usual procedure is to determine, first of all, the percentage of sugar in the blood at the "fasting level," then to administer a dose of 30-50 g. of glucose and make further estimations, say, every 20 to 30 minutes for two hours. Micro-methods are practically always employed, the blood being obtained from a prick of the finger. After trying a number of these methods, it was found that those of Bang, MacLean, Folin and Wu, and Mackenzie Wallis and Gallagher were the most satisfactory. Considerable time and labour are required, however, for the routine performance of any one of these. For some time past the writer has been endeavouring to simplify existing methods, especially from the clinical standpoint, and to increase, if possible, their accuracy. After a number of investigations, it was finally decided to use the rationale of the method of Folin and Wu [1918, 1920], and Mackenzie Wallis and Gallagher [1920] as a basis for this purpose. The process evolved has now been in use for some time and has proved to be most satisfactory. It differs in so many points from the original-in the collection and dilution of blood, the type of standard colour, the size of the boiling-tube, the curve of correction for copper reduction, etc.-that a full description is necessary.