342 Food as a Motive Power. [JWY* 



the remainder in that of heat. How it comes about that oxidation 

 inside a capillary is converted into muscular movement outside, we do 

 not know with certainty. The conversion is effected under the con- 

 trol of the nervous system, and we may therefore venture to suppose 

 that some of the force set free during blood-oxidation may. through 

 the agency of the nerves, take the form of electric currents, which 

 are the direct agents in the muscular work. This, however, is little 

 better than a guess, and as such is entitled to very little reliance. 

 The function of the nerves is the most obscure of all physiological 

 problems, and the difficulty which it presents in this particular 

 hypothesis is not greater than that which enshrouds all others on 

 the subject. 



The establishment of Mayer's hypothesis would of course render 

 meaningless the controversy between the followers of Liebig and 

 those of Traube, for as both fats and carbohydrates on the one side, 

 and the products of muscle metamorphosis on the other, are oxidized 

 in the blood, both may equally be supposed to be originators of mus- 

 cular power. It becomes therefore a matter of the utmost import- 

 ance to test Mayer's view by every means we possess. I think it is 

 possible, by an extension of one of his own lines of argument, to 

 approach very near to a demonstration of its truth. He pointed out 

 that the fluid which passed out from the blood through the walls of the 

 capillaries was afterwards returned to the blood through the lym- 

 phatics, and that the quantity of this exudate could therefore be 

 measured by the quantity of lymph. In this way he calculated 

 that not one per cent, of the blood left the blood vessels in the 

 course of the circulation, and he therefore inferred that not less 

 than 99-100ths of the total oxidation of the body must be affected 

 inside the blood vessels. But this argument is not entirely satisfac- 

 tory, for it might be objected that the exudate, small though it was 

 in amount, carried with it a sufficient quantity of oxygen for the 

 oxidation, and therefore for the work of the muscles. I have there- 

 fore suggested another, which appears to me much more convincing. 

 I purposely exaggerate every element of the calculation, in order as 

 far as possible to overstate the case against me. 



The first thing to be done is to estimate the extreme quantity of 

 fluid which can be supposed to exude through the walls of the blood- 

 vessels in twenty-four hours. We have better data for this purpose 

 than Mayer possessed. Bidder and Schmidt estimate the quantity 

 of lymph and chyle together daily added to the blood at 28 j lbs. 

 Of this 6 J lbs. is chyle, which comes from the food, and may be left 

 out of the calculation. But I will assume the quantity of lymph 

 alone to be 30 lbs. It may be objected that some of the exudate may 

 return directly to the capillaries without traversing the lymphatic 

 system. If this be the case, the quantity so returned could not be 

 large, as the blood flows at a considerable pressure — a pressure 



