This, Professor Flint claims, shows that the work performed was accomplished at the expense of muscular tissue, which was destroyed and caused the increase in the relative excretion.
Were the data as to food more exact, this might be the case; but, as it is, the result seems to need further confirmation before it can be accepted.
The only other similar result, so far as we know, is one recently obtained by E. von Wolff in experiments on the horse; but, having access only to a brief abstract, we are unable to judge of the accuracy of the work, though from the high reputation of this investigator it is to be assumed that it was executed with every precaution. It was found that an increase of the work performed was accompanied by an increased excretion of nitrogen in the urine; but the author reserves the details of his experiments till further observations shall have confirmed or disproved their results, and at present, until the subject has been more thoroughly investigated, we must follow the preponderance of evidence, which is most decidedly in favor of Voit's result, viz., that work does not increase the destruction of proteine in the body and the consequent excretion of nitrogen through the kidneys.
Thus far we have simply been considering experimental results, without regard to the conclusions to be drawn from them; we now come to their interpretation, and here it must be admitted, at the outset, that the data now at command are not sufficient to enable us to solve the problem of the source of muscular power. But, though we do not know precisely what the proximate source of muscular power is, we are able to indicate with tolerable certainty the direction in which an answer to this question is to be sought, and to say that certain conclusions have a high degree of probability.
It would seem at first thought that if, during work, the oxidation of non-nitrogenous matters in the body increases, while no more proteine is destroyed than during rest, the non-nitrogenous matters must be the source of the power exerted. This appears to be Professor Flint's view, as indicated by several passages in his book; but, though it may be a probable conclusion, it is by no means a necessary one. We have already mentioned the fact that Voit and his followers still consider the constant decomposition of circulatory proteine which goes on in the body to be the source of muscular power, comparing it to a constantly flowing stream, the energy of which may be converted at will into motion, or be allowed to take the form of heat; and there is nothing in the experimental results above adduced to forbid this interpretation.
It has been shown by Voit and Pettenkofer to be at least very probable that proteine in its decomposition in the body takes up the elements of water and splits up into urea and fat; and it is easy to show by calculation that 100 parts of proteine could produce in this way 51·4 parts of fat. This process, now, takes place during rest, and it is quite con-
