Bio-Strath is a Swiss Herbal Yeast Tonic clinically proven to recover lost vitality when tired, run down or recovering from illness. Bio-Strath is known to work by improving the lymphocyte (white blood cells, the body's army of defence) response. <p> Usually during a bacterial infection the number of lymphocytes falls. Treatment with Bio-Strath causes a significant increase in the number of all types of lymphocyte.When illness strikes the lymphocytes also act much more efficiently. Bio-Strath works most effectively when the immune system is at its weakest.