462 



Mr. W. North. The Influence of 



Sample of flour | j 



Dried meat |jj 



f 13 



Dried meat < 



ii 



{I 



!! 



Flour . 

 Potato 

 Milk. . 



515 per cent. 



510 „ 

 60 



66 „ 



52 „ 

 58 



70 „ 

 69 



961 „ 



961 „ 



46 „ 

 48 



Phosphates were always estimated in the ash as magnesic pyro- 

 phosphate. 



Sulphates were determined in the ash in the usual way. The deter- 

 minations have little bearing on the results of the experiments, 

 except in so far as they show that the sulphuric acid in the urine has 

 its origin chiefly from sulphur taken into the body in some other 

 form. The determination of the total sulphur in the food would have 

 been of little nse unless the total sulphur of the excreta had been 

 determined also, and, as before stated, this was found to be quite 

 impossible. 



The Work. — Perhaps of all the considerations involved in researches 

 of this kind, the nature of the work done presents the greatest diffi- 

 culties. We are obliged to choose between certain ordinary forms of 

 exercise and the use of machines for the purpose. Each has its 

 advantages and disadvantages, and in all it is well nigh impossible 

 to determine with any reasonable approach to accuracy the total 

 amount of work done. The external work does admit of calculation 

 within limits, but our information with regard to the internal work 

 of the body is scanty and unreliable in the extreme, and in the present 

 state of our knowledge all that can be done is to eliminate the diffi- 

 culty by making the internal work, as far as possible, a constant. It 

 is manifestly unfair to compare walking with the lifting of heavy 

 weights or either with rowing or bicyling ; in none of these forms of 

 labour are the same muscles used, and it is not only possible, but 

 very probable, that different individuals use their muscles differently 

 in each case ; nay, more, that the same individual, unless he is con- 

 stantly practising, does not use exactly the same muscles on different 

 occasions. Walking exercise is, perhaps, the least objectionable of 

 all, and probably for this reason it has found most favour with inves- 

 tigators of this problem, and for this reason I have adopted it in these 

 experiments. 



It might appear that the same distance walked over the same roads, 



