1. Sulfite in concentrations of 0.1% (615 p.p.m. as SO2), or more, in the diet was toxic to rats. Amounts of sulfite less than 0.1% (615 p.p.m. as SO2) in the diet had no significant effect on growth. The rats on the 0.05% (308 p.p.m. as SO2) sulfite containing diet grew more rapidly and had greater gains in weight for the first 12 weeks; however, these gains were not maintained up to the end of the year.
2. There was a definite trend toward smaller average weights and smaller gains in weight of the animals as the sulfite in the diet increased from 0.1% to 2%.
3. Rats fed diets containing sulfite with the addition of thiamine given hypodermically showed growth curves very similar to those of rats on these same diets without the added thiamine.
4. The addition of sulfite to the diets produced deleterious effects over and above those produced by the removal of the main source of thiamine.
5. Sulfite in concentrations of 0.25% (1538 p.p.m. as SO2), or more, decreased the average survival time.
6. The lowest level of sulfite in the diet which produced histopathological changes was 0.1% (615 p.p.m. as SO2).
7. The gross and microscopic pathological changes in the rats on 0.25% (1538 p.p.m. as SO2) or more, of sulfite in the diet included stunting of growth, clinical polyneuritis, "spectacle" eyes, bleached incisor teeth, brown uteri, atrophy of various viscera, calcified renal tubular casts, atrophy of bone marrow and bone, and less frequently focal myocardial necrosis and fibrosis and gastric squamous epithelial hyperplasia.
8. Aging of the sulfite-containing diets caused a decrease in growth rate during the first 12 weeks and an increase in the incidence of lesions of the teeth and uteri, while it had no significant effect on the incidence of polyneuritis.
9. Sulfate and sulfide in the concentrations used in this experiment produced no growth or histopathological changes.