Fasting rabbits were given cocaine hydro-chloride in fever-producing doses (20-30 mgm. per kgm.) ; in 5 the insensible weight loss and in 4 the gaseous metabolism was determined. Water loss was practically identical with total insensible loss until the fever was well advanced. There was a delay in the rise of the vaporization: metabolism ratio corresponding in time to the period previously found at which occurs maximum liver hydration; evidently the ratio begins to rise as the excess water leaves the liver again. In an average case a 2-kgm. rabbit with cocaine lever loses an excess of 3 or 4 cc. per hr. by evaporation, while the liver is yielding its excess water at the same rate. The retention of water by the liver in the 1st stage of fever seems to play a leading role in the interference with heat elimination which causes the febrile temp.