248 Milk and Its Products 
a correspondingly retarding effect. Thus, the develop- 
ment of lactic acid by rendering the lime salts more 
soluble hastens the action of rennet on the milk. On 
‘the other hand, when milk is heated to a tempera- 
ture above 150° F. a part of the lime salts is made 
insoluble, and the action of the rennet correspond- 
ingly retarded, even though the milk be again cooled 
to a temperature at which rennet is active. The 
eoagulability of milk is similarly affected by the addi- 
tion of any lime salt not normally present in milk. 
Thus, if calcium oxalate or other insoluble salt of 
lime is added to milk, the action of rennet is 
retarded. On the other hand, the addition of cal- 
cium chloride or other soluble salt is followed by a 
quicker action of the rennet. 
The rennet skin should be obtained from an 
animal of some age. Still-born calves, or calves less- 
than three days old, furnish a rennet of very inferior 
quality. The calf should be slaughtered three or 
four hours after it has had a full meal, and the 
fourth stomach carefully taken out. This should be 
emptied by turning inside out and any particles 
of foreign matter carefully picked off; it should 
not be washed with water. It should ‘then be 
sprinkled with salt and stretched in such a manner 
that it will readily dry. 
At the present time the preparation of the rennet 
extract from the skins is entirely a commercial one, 
and rennet so much superior, on account of its 
uniform strength and freedom from taints, is fur- 
nished in this way that it is not advisable to prepare 
