Journal of Agricultural Research 
Vol. V, No. 3 
114 
cooled, and made to its original volume; and to the third, 5 c. c. of dis¬ 
tilled water. Another set of three test tubes was prepared with the same 
proportions of materials, but using a 1 per cent solution of Witte's peptone 
in place of the albumin solution. The tubes so prepared were kept in an 
incubator at 40° C. for 24 hours. At the end of this time an aliquot of 
each mixture was drawn off and the quantity of amino adds present in it 
determined by the ninhydrin method recently proposed by Harding and 
MacLean (7), using a solution of glutamic add containing the equivalent 
of 0.1 mgm. of nitrogen in the amino-acid form per cubic centimeter for 
the production of the standard color. 
The characteristic color due to amino adds appeared in all the tests 
except the one in which only water and albumin were used. The amino- 
add equivalent in each case, as determined by comparison with the stand¬ 
ard color, is given in Table VII. 
Tabee VII .—Tests for proteases in the flesh of apples 
Material. 
Amino-acid 
equivalent after 
action (milli¬ 
grams of ni¬ 
trogen). 
Unboiled juice + egg albumin.. 
O. 12 
Boiled juice + egg albumin. 
Water + egg albumin. 
* 
None. 
. 10 
. 10 
Unboiled juice -+■ peptone. 
Boiled juice -f- peptone. 
Water + peptone. 
07 
It appears from these data that both the juice itself and the peptone 
used contained amino acids which would give a blue color with the nin¬ 
hydrin reagent. But the incubated mixture of unboiled juice and albu¬ 
men contained more amino acids than that in which an equal volume of 
boiled juice was used; while with peptone no increase of amino add was pro¬ 
duced by the unboiled juice, and the total amino acid found was just equal 
to the sum of that found in the quantity of juice and of peptone solution 
used in the tests. It thus appears that the juice extracted by grinding 
with quartz sand contains a small amount of some protdn-splitting 
enzym of the trypsin or papain type rather than of the erepsin type. It 
was concluded, therefore, that the flesh of the apples contains a small 
amount of protease, to the action of which on the protein material of the 
apple cells is due the small amount of amino add found to be present in 
the juice of the ripening fruit. 
PECTINASES 
The fact that the flesh of an apple softens and becomes mealy or mushy 
at the close of the ripening period is generally attributed to the solution 
of the middle lamella and the consequent separation of the cells of the 
tissues. The solution of the middle lamella is supposed to be the work 
of an enzym known as pectinase. It is supposed, therefore, that pecti- 
