A HARD-WORKING DIET. 29 
as a fact and practically acted upon in public dietaries 
and by artizans and navvies, who, without knowing 
anything of carbon and nitrogen, eat what experience 
tells them they require. (See Appendix.) 
It is only within the last fifty years, roughly speak- 
ing, that any attention has been paid to the proportion 
of carbon, hydrogen and nitrogen in foods, and only 
quite recently—since 1866—that the work they do in 
the body, and the amounts of them needed for different 
kinds of work, has been understood. 
It may perhaps seem leaving the immediate subject 
of “Fish in Diet” to pause to allude to this at all, but 
it will be seen that unless the values of different foods 
in general use is understood, the relative value of any 
particular food, whether beef, mutton, bacon, or fish, 
cannot be understood. Further than this, there is a 
wide difference in the values of different kinds of fish. 
Though it would add much to the interest of under- 
standing this modern study to go through the history 
of how it came about, it would take time, and it is not 
essential to understanding the present views. 
Chemistry cannot explain everything with regard eens es 
to the connection between food and work. There is digestion. 
that mysterious connection between thought and 
digestion and digestion and thought. We cannot say 
give a man so much C and N and he will be able to 
do so much muscular work. The receipt of depressing 
news may quite upset his power to eat the food or 
to digest it, and the C and N must be zz the blood 
before it can be of practical use, so that the mere fact 
of eating so many ounces of carbon and_ nitrogen 
compounds does not necessarily imply the power to 
do work. All that chemistry can do is to show what 
