DIGESTIVE ENZYMES IN POIKILOTHERMAL VERTEBRATES 
185 
Among the reptiles glands have not been found in the esophagus of Sauria and 
Ophidia, but have been described in the lower portion of the esophagus of certain 
Chelonia and Crocodilia (Oppel, 1897). 
Decker (1887), using the disappearance of fibrin in dilute hydrochloric-acid 
extract as his criterion of peptic digestion, reported "peptic digestion" in the 
esophagus of fishes as of general occurrence. Biedermann (1911) believed that 
Decker mistook the sunple action of acid upon fibrm for peptic digestion. It may 
be that Decker failed to thoroughly clean the esophagus from pepsin-laden fluids 
backing up from the stomach. It seems to the writer also possible that what Decker 
thought was peptic digestion may have been digestion by autolytic enzymes, which 
act in sufficiently dilute acid but are practically, inhibited at a hydrogen-ion concen- 
tration of a pH 3 to 2.5, at which pepsin acts most rapidly. Observations that have 
been reported of small fishes digesting within the esophagus of larger fishes (such as 
those reported by Spallanzani, 1785) probably indicate merely digestion by gastric 
juice flowing forward into the esophagus. 
STOMACH 
Table 1 is a comparative record of results obtained for the rate of peptic digestion 
upon coagulated egg albumin by extracts from representatives of different classes of 
vertebrates. Increase of tyrosine is taken as the chief criterion for initial cleavage. 
While amino-acid production in gastric digestion is too small to be measmed with 
any high degree of accuracy, it is interesting to note that there is slight increase in 
amino acid in each digest and to compare the amoimt produced here with that 
produced in tryptic and ereptic digestion (Tables 3 to 6). 
Table 1. — Rate of peptic digestion in different groups of vertebrates 
[Parallel digests with boiled extracts were ran for each animal. Only two controls are included in the table to save space, since 
all controls produced no tyrosine or amino acid. Room temperature averaged 23 to 26° C. Each digest consisted of the 
following proportions: 12.5 c. c. extract of stomach mucosa (except carp) +20 c. c. coagulated egg albumin+0.2 N HCL (about 
15 c. c.) to approximately pH 3 to 60 c. c. total] 
Animal 
Fish: 
Carp control 
Alimentary tract to first bend 
Posterior to first bend 
Bluegill etent 
Crappie do-. 
Pickerel do.. 
White bass do.. 
Amphibia: Necturus do-. 
Reptile: 
Painted turtle _ do.. 
Snapping turtle __ __do-- 
Bull snake _ _.do-. 
Mammal: Dog do-- 
Num- 
ber of 
tests 
Milligrams tyrosine in 2 c. c. Citrate 
Days 
0. 087 
.079 
.067 
. 154 
. 154 
.143 
.094 
. 175 
.131 
.091 
.088 
. 122 
.222 
0. 087 
.119 
. 125 
. 154 
.418 
.400 
.364 
.435 
.461 
.428 
.478 
.467 
0.087 
.120 
144 
. 154 
.424 
.446 
.422 
.349 
.444 
.476 
.456 
0. 087 
.120 
. 144 
. 154 
.446 
.440 
.396 
.462 
.493 
.470 
.506 
.500 
0. 087 
. 120 
.150 
. 154 
.467 
.472 
.452 
.456 
.468 
.605 
.626 
.506 
.500 
Net 
gain, 
8 days 
0. 000 
.041 
.083 
.000 
.313 
.329 
.358 
.281 
.337 
.414 
.438 
.384 
.278 
C . c. 0.2 N amino acid 
in 10 c. c. filtrate 
Days 
0.100 
.083 
.125 
.100 
.100 
.150 
.116 
.0.50 
.125 
.100 
. 100 
.100 
.200 
0. 100 
. 133 
.225 
.100 
.450 
.500 
.300 
.200 
.360 
.400 
.325 
.625 
.500 
Net 
gain, 
8 days 
0.000 
.050 
.100 
.000 
.350 
.350 
.183 
.150 
.225 
.300 
.225 
.425 
.300 
With the exception of the carp (the only animal used having no well-formed 
stomach) all the animals showed a remarkably uniform rate of digestion. Since 
the carp differs so widely in anatomical structure and activity, it will be discussed 
