1. No destruction of pepsin by heat is demonstrable at pH 1.6 until a temperature of 40°C. is exceeded.
2. The influence of the backward reaction in peptic hydrolysis is shown in the diminishing rate at which increasing concentrations of protein are hydrolyzed.
3. The backward reaction causes the optimum for the hydrolysis of higher concentrations of protein to be attained at a lower temperature than with more dilute solutions.
4. The proteose and peptone associated with commercial pepsin retard hydrolysis in the same sense as the products due to the action of the enzyme.