Preparation of Rennet., 171 
fourth or digestive stomach of a calf that has not 
yet ceased to live upon milk, though rennet is also 
found in the stomachs of puppies and pigs, and the 
latter have come to be of almost equal importance 
with calves as a source of rennet. The active prin- 
ciple of the rennet is found in the folds of the 
lining membrane of the stomach of the animal, and 
is greatest in amount when a full meal is just di- 
gested. The rennet should be obtained from an ani- 
mal of some age. Still-born calves, or calves less 
than three days old, furnish a rennet of very in- 
ferior quality. The calf should be slaughtered three 
or four hours after it has had a full meal, and the 
fourth stomach earefully 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 stretehed 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 aecouut of its 
uniform strength and freedom from taints, is fur- 
wished in this way that it is not advisable to prepare 
the rennet for use from the skins. In the prepara- 
tion of the extract, the skins are soaked in warm 
water to which a little salt has been added until the 
active principle has been completely removed from 
them. The resulting extract is filtered, and preserv- 
atives, in the shape of salt and a little saltpetre, 
are added. Rennet so prepared will retain its 
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