NUTRITION 
with hydrogen as a definite radical, NH 2 , known as the amide radical. 
It may replace an H or OH group in the various carbohydrates and their 
allied acids, converting them by this slight change into quite different 
substances. 
Thus, either acetic acid, CHs COOH, or glycolic acid, CH a OH COOH, be- 
comes amido-acetic acid (glycin), CHgCNH^) COOH, by the substitution of the 
amide radical NHj for hydrogen (H) or hydroxyl (OH), respectively. Glucose, 
COH CHOH CHOH CHOH CHOH CH 2 OH, becomes glucosamin COH 
CH(NH 2 ) CHOH CHOH CHOH CH 2 OH, by a like substitution. On the 
other hand, some of the constant decomposition products of the more complex 
CHsv 
proteins are glycin (ante); leucin, )CH CH CH(NH 8 ) COOH ; tyrosin, 
CHg/ 
HC CH 
OH C^ J?C CHa CH(NH 2 ) COOH; asparagin, CO(NH a ) CH(NH 3 ) 
HC=CH 
CHj COOH; in all of which the amide radical has replaced H or OH of an allied 
substance. 
Proteins. Proteins are the substances which compose the larger part 
of the cytoplasm; protein foods, therefore, are those which can be most 
directly used for nourishment, and so represent the end of food making. 
To define proteins is quite impossible; they are so numerous and so 
varied that scarcely any characteristic is universal. Within this huge 
group are included some substances which are relatively simple, and 
others whose complexity defies all analysis. Even the simplest are 
scarcely known chemically, the actual knowledge permitting only theo- 
ries of their construction. It has been possible in most cases to deter- 
mine only the percentage composition, which with a study of the decom- 
position products sometimes permits the establishment of an empirical 
formula. The more complex proteins contain sulfur, and some have 
also phosphorus in addition to the carbon, hydrogen, oxygen, and 
nitrogen of amides, with traces of ash, which may or may not be struc- 
turally a part of the protein. One nearly pure protein is familiarly 
known, the albumin or " white " of eggs; perhaps the best known plant 
protein is the one longest known, the gluten of wheat grains. 
To illustrate the complexity of these substances and, as well, the uncertainty re- 
garding their composition, the following formulas, though hardly more than guesses, 
are quoted. A crystalline vitellin from squash: C22H48iN9 O83S2. An albumin: 
C72oHns4N2i8O248S6- Hemoglobin (of the blood): C7i2HiisoN2i4O2tfFeSt; the 
same, another guess, ' 
