212 TWENTY-FIFTH ANNIVERSARY REPORT. 
2. CHANGES IN CHEESE CAUSED BY RENNET-ENZYM. 
Rennet extract contains an enzym which is a peptic ferment, as 
shown by the following characteristics: (a) Neither rennet-enzym 
nor pepsin causes much, if any, proteolytic change except with the 
help of acid; (b) the quantitative results of proteolysis furnished 
by rennet-enzym agree closely when working on the same material 
under comparable conditions; (c) the classes of soluble nitrogen 
compounds formed by the two enzyms are the same both quali- 
tatively and, under uniform conditions, quantitatively; (d) neither 
enzym forms any considerable amount of amido compounds and 
neither produces any ammonia; (e) the soluble nitrogen com- 
pounds formed by either enzym are chiefly confined to the groups 
of compounds called paranuclein, caseoses and peptones (Bul. 
No, 233). 
In normal cheese, we find an accumulation of amides and ammo- 
nia, as the cheese grows older and a corresponding diminution 
of the compounds previously formed. The formation of all the 
ammonia and of a large proportion of the amides found in ripened 
cheese must be due to some agency other than rennet-enzym, and 
the only other agents present, besides milk-enzyms, that can do 
this work appear to be organisms or their enzyms. The first stage 
in normal cheese-ripening is essentially a peptic digestion of para- 
casein or some derivative compound. Gradually amides are formed 
and later ammonia. It is probable that the first chemical work done 
in normal cheese-ripening is the conversion of paracasein or some 
modification of it by rennet-enzym into paranuclein, caseoses and 
peptones.. The question naturally arises as to whether these com- 
pounds must be formed before other agents can take part in the 
work and carry it along farther, producing amides and ammonia. 
A COMPARATIVE STUDY OF DIFFERENT BREEDS OF 
DAIRY COWS. 
In 1889 an extended investigation with different breeds of dairy 
cattle was undertaken which had for its object a comparison of 
seven different representative breeds with reference to economy of 
milk, butter and cheese production. The work was continued for 
about seven years. The breeds of cows used in the investigation 
were American Holderness, Ayrshire, Devon, Guernsey, Holstein- 
Friesian, Jersey and Shorthorn. The following detailed data are 
given in the Station reports for the years 1890 to 1896: (1) Tabu- 
