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Since glucuronic acid and glucosamine are characteristic constituents of the prosthetic group of mucin, the biochemical synthesis of mucin can not take place without them. Very little is known about the metabolism of these substances, except that they are probably not glycogenic and are surprisingly inert in the body. We are interested in studying the metabolism of these substances because their metabolism is so closely related to the metabolism of mucin and gastro-intestinal function.We wish to report our findings to date. When dogs are fed borneol, it is excreted as borneol glucuronic acid. In another paper of this series, Miller and Conner show that the glucuronic acid arising from the digestion of mucin in rabbits is readily available for conjugation with menthol, and that either the rabbit is unable to synthesize glucuronic acid from carbohydrates or amino acid metabolites, or that the synthesis takes place slowly. We were interested in determining if this applied to dogs.Three dogs having an average weight of 9.5 kg. were fed a stock diet of bread and corn meal gruel containing a little meat broth. They were given 5 gm. of borneol in 90 cc. of 1% agar by stomach tube for 31 successive days. Their average total excretion of glucuronic acid as borneol glucuronic acid was 30.78 gm. Their average daily excretion of glucuronic acid was 1.11. gm.∗At the end of the experiment their average weight was 8.12 kg. During the last 8 days the average daily excretion was 0.63 gm., which is lower than the average daily excretion for the entire period. The dogs were then fasted for 5 days, but the daily administration of borneol was continued.

It is generally considered that the animal body can synthesize glucuronic acid either from carbohydrates or from amino acid metabolites. Miller and Conner have reported results previously which indicate that either the rabbit cannot synthesize glucuronic acid or that the rate of synthesis is low. A similar investigation on dogs did not give such definite indications. In comparing the chemical properties of glucuronic acid with the chemical properties of Vitamin C, we were struck with the close similarity existing between them. Svirbely and Szent-Györgyi1have reported evidence indicating that Vitamin C is an hexuronic acid. Glucuronic acid is an hexuronic acid and we decided to compare its biochemical properties with those of Vitamin C, even though Hirst and Reynolds2state that the hexuronic acid isolated by Svirbely and Szent-Györgyi is not glucuronic acid. We were interested also in the importance of glucuronic acid in growth.If glucuronic acid cannot be synthesized by the growing animal, it would then be an essential carbohydrate acid for growth, for it is a constituent of the glycoproteins in cartilage, connective tissue and mucin. If glucuronic acid can be synthesized by the growing animal, then they should experience no difficulty in growth on a diet deficient in glucuronic acid.Eighteen guinea pigs weighing 280-320 gm. were fed the basal Vitamin C deficient diet of Sherman, LaMer, and Campbell,3ad lib.Of these, 6 were fed, by dropper, a water solution containing 2 mg. of an equilibrium mixture of glucuronic acid∗and its lactone, for 9 days, and thereafter 10 mg. per day. Six were fed 1/4 gm. of gastric mucin per day, mixed with dry feed, and 6 were kept as controls.

The antiscorbutic properties of various substances related structurally to ascorbic acid have been investigated and reported. We have investigated the antiscorbutic properties of methyl-2-keto-gluconate.Sixteen guinea pigs, between 250 and 300 gm. in weight, were placed on a modified Dutcher scorbutic diet1consisting of rolled oats, white wheat flour, and alfalfa flour. They were fed 3 cc. of orange juice daily for 7 days before the start of the test experiment. During this time they showed a constant daily gain in weight. They were divided into 6 groups.Group 1. Three animals. All showed loss of weight in 10-15 days, followed by the appearance of scorbutic symptoms. One was fed 3 cc. of orange juice at the 23rd day, but died of scurvy at the 26th day. The other 2 were fed 50 mg. and 70 mg. daily of methyl-2-keto-gluconate starting at the 23rd day, after which they quickly gained weight, lost their scorbutic symptoms, and grew steadily. At the 41st day the supplement was removed, and they gradually lost weight, developed scurvy, and died at the 53rd and 55th day, respectively.Group 2. Two animals. Began to lose weight at the 10th day, and had developed gross scorbutic symptoms by the 15th and 16th days. On the 20th day one animal was started on 100 mg. of supplement daily, blut died on the 23rd day. The other was given 70 mg. of supplement daily starting at the 20th day. At the 27th day this was increased to 100 mg., and the animal began to gain weight. At the 36th day, when the animal was in good condition, the dose was cut down to 50 mg. daily, and finally discontinued at the 41st day. Scorbutic symptoms developed on the 44th day, and the animal died on the 52nd day.