RAMJI NARAIN AND ATAM SINGH                         227

It will be seen from the above that the optimum temperature for the
action of the vegetable rennet is in the neighbourhood of 70°C. The activity
increases with a rise in temperature up to 70°C. beyond which it shows a falling
off till 80°C. is reached when it is altogether destroyed. Working with rennets
of animal origin Fleischmann [1876] found the optimum temperature of calf's
rennet to be 41 °C., while according to Waksman and Davison [1926] it is 45°C.
Euler [1910] gives it between 37°C. and 39°C.

Chodat and Rouge [1906] find the optimal temperature for syko-chymase
from Ficus carica to be between 75°C. and 80°C., while for rennet from Witha-
nia coagulans it is about 70°C. Evidently the optimal temperature for vege-
table rennets is much higher than for animal rennets and this fact seems to
have some relationship with the body temperatures of animals and plants.
Plants are exposed to the direct heat of the sun which in a torrid climate rises
to about 60°C. or even more. It has been found that the temperature of the
plant is not very widely different from the temperature of its environment and
the period of the metabolic activity of the plant synchronizes with that of the
photosynthetic activity. The economy of the plant therefore demands that
the chemical reactions going on within its tissues should be able to adjust
themselves in accordance with the temperature of its environment. Similar
adjustment of the activity of the enzymes to changes in environmental con-
dition was noticed by Narain [1918] in his studies of the change of activity
of the oxidizing enzymes in the sugarcane as a result of changes in the reaction
of media.

In order to determine the correlation between the activity of the enzyme
and the temperature of reaction mixture, another similar experiment was
performed under strictly controlled experimental conditions at 5°C. intervals
of temperature. In the case of animal rennet it has been found by Grimmer
et al. [1925, 1928] that between the range 20°-38°C. the duration of coagulation
is a logarithmic function of the temperature, of the following form :—

log (d₁ — a) — log (d₂ — a) = C (t₂ — t₁)

where d₁ and d₂ are the duration and t₁ and t₂ are the respective temperatures,
a and c are constants whose values are 25 and 0.05 respectively. This rela-
tionship has been found to hold good in the case of vegetable rennet also
between 30°C. - 60°C. The following figures illustrate the application of this
equation to the calculation of the time of coagulation which compares well
with the actual time observed.

(b) Effect of heat on the activity of the enzyme.—It is commonly known that
rennet kept in boiling water for a few minutes is completely destroyed. In
order to ascertain the changes in the activity of the enzyme kept at different

                                                                                                        E