DIGESTIVE ENZYMES IN POIKILOTHEBMAL VERTEBRATES 
197 
A few tests were made for the presence of maltase and lactase. Maltase was 
found in great abundance in the hepatopancreas but not at all in the small intestine 
of the carp. It was present in small amounts in the small intestine of the snapping 
turtle. Tests for lactase in the intestine of the carp, Necturus, and the snapping 
turtle all yielded negative results. 
GENERAL DISCUSSION 
The relationship of nutritive processes to all the physiological activities of 
organisms makes the importance of obtaining a knowledge of the digestive enzymes 
in all groups of animals apparent. Extensive comparative studies of digestive 
enzymes in representative animals throughout the animal series would be of great 
value. In his comprehensive review of the work done in the physiology of digestion, 
Biedermann (1911, p. 1049) made the following statement in regard to the lack of 
knowledge of digestive processes even in the vertebrates : 
Wenn man von den karnivoren und omnivoren Saugetieren absieht, unsere Kentnisse der 
Ernahrungsphysiologie hier kaum minder diirftig und liickenhaft sind als bei den Wirbellosen. 
The data obtained show that apparently little change in the general character 
of enzymes or their rate of activity has occurred in the evolution of amphibians, 
reptUes, and mammals from primitive types. The rate of peptic digestion of coagu- 
lated egg albumin per given weight of moist stomach mucosa is remarkably uniform 
for the representatives of all classes of vertebrates studied. This substrate is equally 
well digested by the enzymes of fishes, amphibians, reptiles, and mammals. The 
reaction of the stomach in each group of poikilothermal vertebrates is variable, 
usually being acid when the stomach contains food and nearly neutral when the 
stomach is empty. 
A close correlation exists between alimentary structure and the distribution 
of digestive enzymes. The data for the carp (which is a fish without a stomach 
or gastric glands) indicate that no pepsin is secreted by any part of the alimentary 
tract, and that the initial cleavage of proteins in this animal is largely by the trypsin 
from the hepatopancreas. Production of pepsin seems to be limited almost univer- 
sally to a stomach mucosa possessing gastric glands. In a few cases, as in the frog, 
pepsin production has been demonstrated in the esophagus. In this animal, how- 
ever, there is no sharp line of demarcation between the esophagus and the stomach. 
Extracts of esophageal mucosa from the pickerel, bull snake, and snapping turtle 
were tested for pepsin and none was found. While there was indication of a trace 
of pepsin in the intestinal mucosa of the pickerel and the turtle, it was not found in 
the intestine of other animals studied, and in all cases the presence of trypsin in 
any considerable quantity was limited to the pancreas (hepatopancreas in the 
carp). 
The general occurrence of erepsin in the mucosa of the intestine in poikilother- 
mal vertebrates is shown for the first time. This enzyme is present in as great or 
greater abundance in the intestinal mucosa of fishes, amphibians, and reptiles as in 
the intestinal mucosa of the dog. 
Digestion experiments were carried on mainly at room temperature. For 
pepsin, trypsin, and erepsin parallel tests for representatives of each group of the 
