160 Dairy Bacteriology. 



168. Enzyme theory. In 1897, Babcock and the 

 writer 1 were able to demonstrate that milk contains cer- 

 tain inherent unorganized ferments or enzymes that have 

 the power of digesting the casein of milk, when kept under 

 the influence of chemicals that would suppress bacterial 

 action, but which would not materially interfere with 

 enzyme activity. This ferment they find present in the 

 milk of different species of mammalia (burro, horse, 

 sheep, goat, pig, buffalo, and human), and in cows' milk 

 in such quantities that they can isolate it from centrifuge 

 slime. The effect of this chemical ferment which they 

 call galactase, is shown in the breaking down of the nitro- 

 genous matter in boiled milk, forming albumoses, pep- 

 tones, amido acids, and ammonia, products that agree 

 in every way with those present in a normally ripening 

 cheese. This ferment is allied to trypsin, the pancreatic 

 enzyme, and Jensen 2 has recently shown that pancreatic 

 extracts when added to cheese accelerate the digestive 

 changes. 



169. Present status of theory of cheese-ripening-. 

 Comparative experiments on milk and cheese seem to 

 show beyond all question that the breaking down of 

 casein into peptone and related products is due to the ac- 

 tion of this inherent ferment of the milk which is called 

 galactase, and not to the action of bacteria as heretofore 

 believed. Previous investigators have failed to recog- 

 nize the presence of this ferment in milk because they 

 have sterilized the same by heat, and under these condi- 

 tions galactase is destroyed. A brief exposure of milk to 

 176 F. is sufficient to accomplish this result, and even 

 exposures to considerably lower temperature weakens its 

 activity considerably, especially if the reaction of medium 



1 Babcock and Russell, 14th Wis. Expt. Stat., p. 161, 1897. 

 8 Jensen, Cent. f. Bakt., II. Abt., 3: 752. 



