The results obtained with the low protein diet were strikingly different from those of the first two experiments. In this experiment the same groups of mice were placed on a diet of whole, shelled corn for a period of six weeks. The corn contained less than 11 per cent protein, about three per cent fat, and about 80 per cent carbohydrate. By the end of the first week, on the low protein diet, all mice had reduced their water intake by about half the amount used per day on the high protein diet (Table 7). There was not a statistically significant difference, for either species, between the average amounts of water drunk in the first and in the sixth weeks of the experiment. The data in Table 7 show that on all three diets, individuals of _P. maniculatus_ drank less water per gram of body weight than individuals of _P. truei_. Variation in water consumption was high; some individuals of _P. maniculatus_ that drank more than the average amount for the species, consumed as much water as some individuals of _P. truei_ that drank less than the average amount. In general, individuals of _P. maniculatus_ drank about half as much water each day as individuals of _P. truei_. Individuals of both species were consistent in their day-to-day consumption. TABLE 8--Amounts of Mean Daily Water Consumption as Reported in the Literature for Species of _Peromyscus_. Figures in Parentheses are Means; Those Not in Parentheses Are Extremes. Column headings: A: Mean daily ml./gm. wt./day B: Water consumption total ml. per day C: Temperature D: Humidity E: Per cent dietary protein F: Investigator