1867.] Food as a Motive Power. 343 



which would tend to prevent such a return. Nevertheless, I will, 

 on this supposition, double the amount already given, and take it at 

 60 lbs. A large proportion of this would arise from glands and 

 other parts which do Little or no muscular work ; but this I neglect. 

 Finally, it may be urged that some portion of the exudate may 

 escape as perspiration without returning to the blood at all. I 

 therefore add 6 lbs. to obviate this source of error, and thus get a 

 total daily exudate of 66 lbs. or 30 kilogrammes, an amount which 

 I think every physiologist will admit is an extreme overstatement. 



How much oxygen can possibly be supposed to pass out in 

 solution in this 30 kilogrammes of exudate ? Berzelius found that 

 the serum of blood would not dissolve more oxygen than water 

 would. This would give as the quantity of oxygen exuded in 

 24 hours, less than 1^- grammes ; but I will assume that the 

 exudate will dissolve 20 times as much oxygen as this, in fact, that 

 it will absorb more than the moist corpuscles of the blood of the 

 portal vein, which are superior to all others in this respect. The 

 estimate is so extravagant that it is almost absurd to make it. It 

 gives, as the daily exudate of oxygen through the muscles, 25*74 

 grammes. If the work of the muscles is done by oxidation outside 

 the walls of the capillaries, it must all be done by this quantity of 

 oxygen, and it is easy to show that the quantity is entirely insuffi- 

 cient for the purpose, whether it were employed in the oxidation of 

 muscle or of fat. 



25*74 grammes of oxygen would oxidize 17*31 grammes of 

 muscle, and thus yield a force of 31,210 metre-kilogrammes, or 8 -87 

 grammes of fat, and thus yield a force 34,070 metre-kilogrammes. 



To compare with this I will give an extremely low estimate of 

 the work accomplished in the body in 24 hours, omitting doubtful 

 items : — , ", ., 



Metre-kilogrammes. 

 Work of the heart (Donders) . . . 70,000 



Work of the lungs 10,000 



Work of the muscles .... 20,000 



100,000 



The force actually generated to effect this work must, as Haiden- 

 hain has shown, be at least double the above quantity, so that even 

 upon this extravagant calculation, the oxygen, which may be sup- 

 posed to pass out from the capillaries to the muscular tissues, can 

 only account for about one-sixth of the work done by the muscles. 



The establishment of Mayer's hypothesis would unfortunately 

 not help us much in the solution of the practical question, What 

 kind of food is most suitable for the man who does hard work ? 

 Both flesh-formers and heat-givers are available for the purpose, and 

 provided the former are sufficient to repair the daily waste of the 

 tissues, it is possibly immaterial which is employed. Even this, 



