192 TWENTY-FIFTH ANNIVERSARY REporT. 
(4) By utilizing the combination of paraffining cheese and curing 
it at low temperatures, the greatest economy. can be effected. 
3. CONDITIONS AFFECTING CHEMICAL CHANGES IN CHEESE-RIPENING. 
It is well known that, during the cheese-making process, chemical 
changes soon begin in the freshly coagulated curd or calcium para- 
casein, which is formed when milk-casein is acted upon by rennet. 
These chemical changes in paracasein are followed by others, and 
we have a series of such changes from the time the cheese-making 
process begins, continuing for many months. The same cheese ex- 
amined at intervals is found to show quite marked variations in the 
character of its nitrogen compounds. Cheeses made from the same 
milk under the same conditions of manufacture and subjected to 
different conditions during the ripening process show a difference 
in chemical composition. Cheeses manufactured under different 
conditions and ripened under uniform conditions may vary in the 
character of their nitrogen compounds. It was desirable that a 
somewhat comprehensive study should be made of the changes 
actually found in the nitrogen compounds of cheese, using in the 
work only cheeses made and ripened under known, controlled con- 
ditions. The study extended to some of the more prominent factors, 
such as time, temperature, moisture, salt, rennet, acid, etc. 
Starting with the casein of milk, we have in cheese-curd and in 
ripening cheese the following nitrogen compounds formed in some- 
thing like the following order: paracasein, paranuclein, caseoses, 
peptones, amido compounds and ammonia compounds. Paracasein 
is soluble in 5 per ct. solution of salt, while the other compounds 
are soluble in water. Among the amido compounds there have been 
found (Bulletins 219, 231) the following: Lysatine, histidine, 
lysine, tetramethylenediamine (putrescine) ,tyrosine, oxyphenylethyl- 
amine, arginine, guanidine, etc. The amounts of these different 
compounds and classes of compounds and their relations to one 
another will be briefly considered. 
(1) The relation of time to the cheese-ripening process—The 
amount of water-soluble nitrogen increases as cheese ages. The 
rate of formation of these compounds is more rapid in the early 
stages of ripening, about 66 per ct. being formed during the first 
three months and over co per ct. in the first nine months of an 
eighteen-month period of study. The data upon which these state- 
ments are based are contained in the following table: 
