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