350 ON THE PLACE OF FISH IN 



to see on a frosty day that there is more water in the 

 air we breathe out than that we breathe in. As we 

 breathe out, then, more carbonic acid and water than 

 is in the air we inhale, we know that carbon and 

 hydrogen are being oxidized somewhere within the 

 body. This oxidation gives rise to heat (p. 337) 

 and heat and motion go together. 



This may suffice as a rough and ready way of know- 

 ing by observation what are the principles on which 

 calculations as to C, H, O, and N, in foods are based. 

 The principle Experiments have, however, been carried further 



is the same in ,, . . , . . . 



scientific work than this not simply to find that carbonic acid and 

 arrangements water are formed by oxidation in the body, but how 

 elaborate much of each is formed. To do this of course requires 

 special arrangements. For example, Dr. Edward 

 Smith, in ascertaining how much carbonic acid was 

 given off during exertion of different degrees, wore a 

 sort of mask covering his nose and mouth, and a 

 flexible tube carried his breath to his apparatus for 

 ascertaining the weight of water and carbonic acid 

 given off in certain time. Pettenkoffer carried out 

 observations on a watchmaker who consented to 

 work inside a case, one day doing no harder work 

 than reading, another, doing his usual light work of 

 watch-fitting, and another day working a treadle. The 

 amount of food and of oxygen admitted to him, and 

 of carbonic acid and water, &c., given off, were 

 accurately weighed. 



The experiments of Pick and Wislecanus are men- 

 tioned in Appendix. The two mentioned here may 

 serve as examples that the statements and figures 

 given by scientific chemists about "the C, H, and N 

 taken in as one set of compounds in food, and given 



