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 ; 



