818 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 
regularly carried on in the chemical laboratory in the analysis of meat 
and other food materials. Portions are dried with proper apparatus, 
and the percentages of water and water-free substances are determined ; 
other portions are burned, and the percentages of ash are found out. 
If we weigh the whole meat, bone and all, to start with, and afterwards 
weigh bone and other refuse and the meat, we can easily calculate the 
percentages of refuse and edible portion. If we then determine the 
percentages of water, water-free substance, and ash in the meat, we 
have made a fair start in the analysis for determining the food value. 
The water-free substance contains all of the nutritive materials, or 
nutrients, but the analysis thus far has told only the percentage of ash, 
or mineral matters. The proportions of tHe other ingredients must be 
found out before we can judge exactly of the food value. 
The meat consists of lean and fat. Part of the fat is in large lumps, 
which can be easily separated from the lean. Indeed we often cut out 
the fat of the meat which is served on our plates at the table, and reject 
it instead of eating it. But a portion of the fat is in very fine particles 
diffused throughout the lean. Much of this finely divided fat is in par- 
ticles so small as to be invisible to the naked eye, but it is possible to 
separate them very completely from the lean by processes of analysis 
common in the laboratory. After the water and the fat have been 
removed from the lean meat the material which remains will contain a 
little mineral matter, which would be left as ash if it were burned ; the 
rest consists of so-called protein compounds. The protein is the chief 
nutritive constituent of fish and eggs, as well as of lean meat. It occurs 
also in milk and in vegetable foods, such as wheat, corn, potatoes, etc. 
Fat is familiar to us in meat, from which we get it in the form of tal- 
low and lard ; in milk, from which it is obtained as butter ; in the various 
oils, such as olive oil, cotton-seed oil, and the oils of wheat and corn. 
Larger or smaller proportions of fat are found in most food materials. 
Potatoes, wheat, and corn contain large proportions of starch. Sugar 
cane and sorghum are rich in sugar. Starch and sugar are very similar 
in chemical composition, and are called carbohydrates. Other carbo- 
hydrates are found in animals and plants; such as inosite, or “muscle 
sugar,” in muscle ; and glycogen, or “liver sugar,” in the liver. 
The mineral matter, or ash, which is left behind when animal or 
vegetable matter is burned, consists of a variety of chemical com- 
pounds commonly called salts, aird including phosphates, sulphates, 
and chlorides of the metals calcium, magnesium, potassium, and sodium. 
Calcium phosphate, or phosphate of lime, is the chief mineral con- 
stituent of bone. Common salt is chloride of sodium. 
The number of the different chemical compounds in our animal and 
vegetable food materials is very large, but leaving water out of ac- 
count, it is customary to divide the rest into the classes of which w r e 
have spoken, to wit, protein, fats, carbohydrates, and mineral mat- 
ters, and to look upon these as the nutritive ingredients, or uutrients 
