58 PRINCIPLES AND PRACTICE OF MILK HYGIENE 



milk which were not members of the coli-aerogenes group 

 but which were apparently spore-formers, having sur- 

 vived a temperature of 93.3 C. (200 F.) for thirty 

 minutes. 1 



3. Peptonizing or Casease Bacteria. The bacteria 

 of this group are also known as liquefiers and are the cause 

 of decay and putrefaction in general. They secrete 

 two enzymes or ferments which attack the proteids of 

 milk, especially the casein. One is a rennet-like ferment 

 which acts upon the calcium casemate in the same manner 

 as rennet, splitting it up into calcium paracaseinate and 

 a substance called whey-proteid. The calcium para- 

 caseinate being insoluble, it is precipitated and forms a 

 curd. The whey-proteid remains in solution in the whey, 

 hence the name. The other enzyme is casease, a proteo- 

 lytic ferment resembling trypsin, which digests the pro- 

 teids in the curd and whey, splitting them up into soluble 

 compounds like albumoses and peptones (peptonization) 

 and then again into simpler compounds like amino-acids 

 and ammonium bases (decomposition). The two fer- 

 ments are produced in varying proportions by different 

 species of bacteria. When the rennet-like ferment pre- 

 dominates a firm white curd is formed and is slowly 

 digested. There is more or less fluid (whey) present. 

 As digestion proceeds, the curd gradually disappears and 

 is replaced by a turbid fluid. The surface of the curd in 

 contact with the fluid has a rough or fuzzy appearance. 

 When the proteolytic ferment (casease) is present in 

 greatest quantity, the curd is soft, flocculent and 

 " mushy," or coagulation does not occur at all, while 

 peptonization takes place rapidly. In the earlier stages 



1 B. A. I. Bulletin No. 161, pp. 47 and 48. 



