INTRODUCTION 11 
changes in color, etc., indicate its constitution ; e.g., 
iron and phosphorus may be detected in this way. 
Parts showing affinity for acid stains like eosin are 
said to be acidophile or oxyphile; those showing 
affinity for basic dyes, like methylene blue, are 
called basophile. The chromatin is _basophile, 
whereas the linin and cytoplasm are oxyphile. In 
macrochemistry large quantities of the substances 
are collected and examined by ordinary laboratory 
methods. 
Because of the importance that has been assigned 
to the chromatin, this substance is particularly 
interesting. Chromatin consists of nuclein, which is 
a conjugated protein containing nucleic acid, the 
latter being an organic acid, rich in phosphorus; 
it is hence called nucleoprotein. Nucleoproteins 
are found chiefly in the nucleus but also occur in 
the cytoplasm. They may differ from one another 
in their protein content as well as in the character 
of their nucleic acid constituent. When treated 
with dilute acids nuclein is obtained, and when this 
is further subjugated to caustic alkali it decomposes 
into protein and nucleic acid. The nucleic acids 
which have been principally studied are those de- 
rived from the thymus gland, and from the sperma- 
tozoa of salmon, herring, and other fish; they are 
probably all the same. Levene (1910) recognizes 
three sorts of nucleic acid, of which the most complex 
is termed thymonucleic acid. This consists of 
two purine bases, guanine and adenine; 
two pyrimidine bases, thymine and cytosine; 
