DIGESTIVE ENZYMES IN POIKILOTHEKMAL VERTEBRATES 
187 
In digests with extracts from the anterior segment and with those from the 
entire posterior part of the alimentary canal production of tyrosine was very small, 
and it seems doubtful whether it was peptic in nature. Since practically all of the 
increase in tyrosine occurred during the early part of experiments, the apparent 
peptic digestion in the carp may have been due to the action of autolytic enzymes 
for a short time before they were entirely inhibited by the hydrogen-ion concen- 
tration of pH 3, which was approximated by the use of congo red indicator paper. 
In studies on autolysis of liver and kidney, Bradley (1922) observed that the maxi- 
mum digestion took place at pH 4.0 to 4.5 (obtained by adding 25 to 40 c. c. of 
0.2 N hydrochloric acid per 250 c. c. of brei), and that digestion by autolytic en- 
zymes was practically at a standstill at a pH of 3 to 2.5 (obtained by the addition 
of 75 to 100 c. c. of 0.2 N hydrochloric acid per 250 c. c. of brei). In the writer's 
experiments about 15 c. c. of 0.2 N hydrochloric acid were added per 50 c. c. digests, 
which would be equivalent to 75 c. c. for 250 c. c. of brei. It would seem possible, 
therefore, should autolytic enzymes of similar character to those of liver and kidney 
be present in the mucosa of the digestive tract, that they might be able to exert 
a slight effect before their complete inhibition. That the digestion by extracts 
from the alimentary tract of the carp was not peptic seems almost certain from the 
fact that in nearly all the digests (cf. also Table 2) no digestion to an appreciable 
extent took place after the first day, though plenty of egg albumin was present 
and conditions were near the optimum for peptic digestion. 
Table 2 shows differences in rates of peptic digestion at 37° C. and at room 
temperature. Except for differences in temperature the tests were made exactly 
as in Table 1. With the exception of the pickerel, where no appreciable difference 
is shown in the rate of digestion at 24 and 37° C, peptic digestion was uniformly 
more rapid at 37° than at room temperature. Moreover, about the same pro- 
portionate increase in tyrosine (initial cleavage) at 37° C. over that at room 
temperature was produced in amphibians, reptiles, and the mammals. 
Table 2. — Peptic digestion at room temperature and at 37° C. ' 
[Digests were prepared exactly as in Table 1, with initial pH 3] 
Animal 
Fish: 
Carp 
Pickerel 
Amphibia: Necturus 
Reptile: 
Snapping turtle.. 
Bull snake No. 1. 
Bull snake No. 2. 
Mammal: Dog.- 
Tem- 
pera- 
ture, 
in de- 
grees 
Milligrams tyrosine in 2 c. c. filtrate 
Days 
0. 078 
.078 
.085 
.085 
. 182 
. ICO 
.101 
. 101 
. 143 
. 160 
.100 
.089 
.222 
.222 
0. 118 
. 100 
.340 
.339 
.435 
.500 
.428 
.470 
.500 
.527 
.455 
. 500 
.407 
.500 
0. 118 
. 105 
.417 
.374 
.453 
.538 
.535 
.582 
0. 118 
. 105 
.441 
.431 
.465 
.500 
.463 
.541 
.535 
.582 
.476 
.556 
.500 
.547 
0.118 
. Ill 
.441 
.431 
.476 
.500 
.463 
.541 
.535 
.582 
.476 
.556 
.500 
.556 
Net 
gain, 
8 days 
0.040 
.033 
. 350 
.346 
.294 
.340 
.362 
.440 
.392 
.422 
.376 
.467 
.278 
.334 
C. c. 0.2 N amino 
acid in 10 c. c. 
filtrate 
Days 
0.05 
.05 
.10 
.10 
. 15 
. 15 
.05 
.05 
.10 
. 10 
.10 
. 10 
.20 
.20 
0. 15 
. 15 
.30 
.25 
.45 
.55 
.25 
.30 
.55 
.65 
.50 
.60 
.50 
.60 
Net 
gain, 
8 days 
0.10 
.10 
.20 
.15 
.30 
.40 
.20 
.25 
.45 
.65 
.40 
.50 
.30 
.40 
27864°— 25 2 
