44 ON THE PLACE OF FISH TN 
Briefly, carbon enters through the mouth as some 
form of compound, becomes oxidized in the body, 
giving rise to heat and force, and leaves the body 
as carbonic acid. 
Hydrogen enters also as some compound, becomes 
oxidized in the body, giving rise to heat and force, and 
~ leaves the body as water, mostly in the breath. 
The amounts given off have to be supplied by foods 
(see p.'23): 
Nitrogen. 
1. The union of N with H forms ammonia. 
2. The N taken into the body in foods leaves it as 
ammonia. 
3. A calculation of the amount of ammonia given 
off tells therefore the amount of N given off. 
4. The amount given off has to be supplied by 
foods (p. 23). 
5. Muscle cannot be formed without N. 
6. It appears ‘from experience that a HARD- 
WORKING DIET must be largely made up of nitro- 
genous compounds—compounds which contain all the 
four elements, C, H, O, N (p. 28). 
These must be accompanied by carbon compounds. 
7. There are some fish, herring, mackerel, sprats, &c. 
(see pp. 32 to 34), which have nearly the same N value 
as beef, mutton, or pork, and, so far as chemistry can 
tell, hard work can be done on them as well as on meat 
8. We are without the direct evidence of experience. 
The average daily requirements of those doing only 
moderate work is (see p. 24) C, 4,900 grains; N, 
300 grains. 
eC 
