With a view to discovering the peculiar role of the anti-beri-beri substance in metabolism Karr (23) studied the effect of specific fasting for this substance upon the desire of dogs to take food. He fed diets which were free from all three well recognized vitamins, and which were composed of isolated food substances, except that commercial casein and wheat gluten were employed as sources of protein. The dogs were restricted to these diets until they refused to take the food. Then a source of the anti-neuritic factor was also allowed them, and was fed separately. Yeast, milk, tomato, and a concentrated extract of water-soluble B were employed for this purpose. It was found that the addition of these substances to the diet resulted in prompt response of the appetite, the animals showing an increased desire for food. Karr concluded that there was some relation between the desire to partake of food and the amount of water-soluble B ingested. Brewery yeast was found much more effective than bakers' yeast for this purpose.

He further studied the metabolism of dogs deprived of water-soluble B, by making quantitative studies of the assimilation of nitrogen from the alimentary tract. No decrease in capacity for digestion, nor in the character of the metabolic products eliminated could be detected as the result of specific starvation for this substance.