Search

RECENT reports have stressed the advantages of using highly specific ‘glucose oxidase’ methods for the clinical determinations of blood sugars1–3. Traditional methods, such as those of Folin and Wu, measure the total reducing capacity of the blood, and include the so-called saccharoid fraction as well as the true glucose-level. The exact nature of this fraction, and its significance in pathological conditions, is not yet fully understood.

HARRIS has showed that the reducing capacity of animal tissues titrated against 2.6 dichlorophenolindo-phenol (as indicated by Tillmans and Szent-Gyorgyi) in acid solution, coincides with the biological activity.

THE conclusion having been reached that vitamin C is identical with hexuronic acid, it becomes of obvious importance in the first place to see how this can be reconciled with Zilva's contention1 that there is a lack of parallelism between antiscorbutic activity and reducing capacity—one of the most characteristic properties of hexuronic acid. Fig. 1 summarises all the data given by Zilva, mean values for antiscorbutic potencies being plotted at each level of reducing capacity. Bearing in mind the unavoidable variation in biological response between individual experimental animals, it becomes evident that Zilva's data, once they are analysed in this way, appear in fact to afford good evidence of a close quantitative relation between reducing capacity and antiscorbutic activity in lemon juice fractions, and therefore are not at variance with the hypothesis that hexuronic acid and vitamin C are identical.

VARIOUS physico-chemical and chemical methods have been used for the determination of vanillin. Of the volumetric methods1, the oxime method has been modified in many ways, whereby either the quantity of the hydrochloric acid set free in the reaction of hydroxylamine hydrochloride with vanillin, or the quantity of the unreacted hydroxylamine, is titrated visually or potentiometrically. Colorimetric methods are based on the slight reducing capacity of phenols2, the polarographic methods3 on the reduction of the aldehydic group of vanillin.

MR. DANN1 is labouring under a misapprehension in interpreting the results of my paper2. My figures show that if the reducing capacity of the various lemon juice fractions be interpreted in terms of fresh decitrated lemon juice, eighteen guinea-pigs receiving daily doses equivalent to 2 c.c. (reduction value 8–10 c.c.), eighteen receiving doses equivalent to 1.5 c.c. (reduction value 6–8 c.c.), thirty-six receiving doses equivalent to 1 c.c. (reduction value 4–6 c.c.), seventy-two animals in all (tested usually three in a group), died of apparently uncomplicated scurvy within 30–40 days. It need scarcely be stressed that young guinea-pigs do not vary in biological response to anything like this extent but always survive much longer than 30–40 days, even if they are not fully protected, on daily doses of 1–2 c.c. or even less of lemon juice. This fact invalidates Mr. Dann's inferences.

THE recent work of Becht and Dresdon1 and Smit2 has brought to light certain histological and physiological features of the slow- and fast-contracting mesothoracic leg muscles of the cockroach, Periplaneta americana. Smit2 has shown that the slow-contracting muscle fibres contain more lipids and possess a stronger reducing capacity for methylene blue than the fast-contracting ones. Histochemical investigation of these two types of fibres3 has shown that there is more lipase activity in the slow-contracting muscles. Here we report the results of a quantitative investigation of lipase activity in the slow- and fast-contracting leg muscles of the cockroach.

THE chemical determination of ascorbic acid is based upon the high reducing capacity shown by this substance with different organic compounds. One of the best known methods based upon this property is the titration of ascorbic acid with 2: 6 dichlorphenol indophenol1, after the removal of interfering substances with mercuric acetate. Others2 have found that ascorbic acid reacts with methylene blue, and this property was made use of for its estimation. This method appears to be the most satisfactory, because the presence of other reducing substances does not interfere with the reactions linked to certain hydrogen ion concentrations. It has, however, certain disadvantages inherent to its colorimetrical nature. It is on account of this circumstance that I have tried to modify this method of estimation and thus to eliminate possible sources of error.

THE indications previously obtained1 that the high reducing capacity of tumours in our dichloro-phenolindophenol test is due principally to a substance other than vitamin C have now been confirmed. In determinations of vitamin C content, by the histological tooth protection method, groups of guinea pigs were given 5 gm. each per day of freshly excised Jensen rat sarcoma (kindly provided by Mrs. Barbara Holmes). The various control groups received 0, 1, 2, 3 and 4 c.c. of orange juice, and 5 c.c. of orange juice plus 5 gm. of sarcoma. The degrees of protection afforded were found to be 1–2 for the sarcoma, 0, 1–2, 2–3, 3, 3–4 respectively for the orange juice controls, and 3–4 for orange juice plus sarcoma (4 = complete protection). It follows that 5 gm. of the tumour is equivalent in vitamin C content to no more than about 1 c.c. of orange juice.