The experiment, however, that came as a death blow to the theories of Liebig was that of Fick and Wislicenus,[43] who in 1865 made an ascent of the Faulhorn, 6500 feet high, using a diet wholly non-nitrogenous. From the nitrogen excreted they were able, of course, to calculate the amount of proteid oxidized in the body during the period of work, and found that the proteid consumed could not have furnished, at the most, more than one-half the energy required to lift the weights of their bodies to the top of the high peak. Further, they observed that neither during the work period, nor immediately after, was there any noticeable increase in the excretion of nitrogen. Obviously, as they state, the oxidation of proteid matter in the body cannot be the exclusive source of the energy of muscular contraction, since the measurable amount of external work performed in the ascent of the mountain was far greater than the equivalent of the energy capable of being furnished by the proteid actually burned. To which may be added the fact that considerable energy, not measurable in their experiment, must have been employed in the work of the involuntary muscles of the body; thus increasing by so much the difference between the muscular work actually accomplished and the available energy from proteid consumed. It is true that minor criticisms regarding certain details of the experiment can be offered to-day, such as the fact that the men were, in a measure, in a state of “nitrogen starvation,” etc., but these criticisms do not in any degree militate against the main thesis that the energy of muscular contraction does not come exclusively from the consumption or breaking down of proteid, either of food or tissue. Vigorous and even severe muscular work does not necessarily increase the decomposition of proteid material. Dogs made to run in large treadmills, with the same diet as on resting days, were found to excrete practically no more nitrogen than during the days of rest. Occasionally, however, in some one experiment the output of nitrogen would show an increase over the output on resting days. Further, experiments made with horses led to essentially the same result, except that greater increase in the excretion of nitrogen was observed than with dogs. This increase in nitrogen output, however, as a concomitant of increased muscular activity, could be prevented by adding to the amount of carbohydrate food. [43] See Gesammelte Schriften von Adolf Fick. Ueber die Entstehung der Muskelkraft. Band 2, p. 85. Würzburg, 1903.