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BULLETIN OF THE BUREAU OF FISHEEIES 
employed. In fact, the greater part of the studies made upon digestion in fishes 
was made before the development of improved quantitative methods and especially 
before the development of accurate methods for hydrogen ion regulation. The 
study of digestive enzymes in amphibians and reptiles has been almost wholly 
neglected. 
The only record that the v.a iter has been able to fixid of any attempt to compare 
the rate of digestion in different groups of poikilothermal vertebrates is that of 
Riddle (1909), which, unfortunately, yielded no conclusive results of a comparative 
nature. 
Recently Bodansky and Rose (1922) published a preliminary study on digestion 
in certain elasmobranchs and teleosts, employing well-controlled hydrogen ion 
concentrations. Using Dernby's (1918) method of liquefaction of gelatin as criterion 
for proteolytic digestion, they found that the optimum pH for gelatin digestion by 
fish pepsin was about 3. This is in agreement with the optimum for mammalian 
pepsin. These investigators found coagulated egg albumin to be very slowly 
digested by the proteolytic enzymes of fishes. From extracts of the pyloric caeca of 
the red snapper (Lutjanus aya) they obtained trypsin, pepsin, rennin, amylopsin, 
and lipsse (weak). Invertase was present to a very slight extent; inidinase, maltase, 
and lactase were altogether absent. 
PURPOSE OF THE INVESTIGATION 
The purpose of the investigations described in the present paper has been 
twofold: (1) To make a comparative study by means of reliable qualitative and 
quantitative methods of the rate of digestion by the more important digestive 
enzymes in representative fishes, amphibians, and reptiles, with less extensive 
studies on those of mammals; and (2) to extend the present knowledge of the 
presence, character, and distribution of proteolytic and carbohydrate-splitting 
enzymes in the animals studied. 
The work has extended over a period of two years. Many of the experiments 
upon fishes were performed while the writer was employed by the United States 
Bureau of Fisheries during the summers of 1922 and 1923. The writer is especially 
indebted to Dr. A. S. Pearse and to Dr. H. C. Bradley, of the University of Wiscon- 
sin, for valuable suggestions and criticisms. 
ANIMALS USED IN THIS WORK 
The following fishes have been used in this investigation: Bluegill, Lepomis 
incisor (Cuvier and Valenciennes); carp, Cyprinus carpio Linnaeus; black crappie, 
Pomoxis sparoides (Lacepede) ; pickerel, Esox lucius Linnaeus; perch, Perca Jlavescens 
(Mitchill) ; sucker, Catostomus commersonii (Lacepede) ; and white bass, Roccus 
chrysops (Rafinesque). Of these the pickerel, as a representative of carnivorous 
fishes, and the carp, that is mainly vegetarian in its diet, have been the most thor- 
oughly studied. The principal amphibian studied was the mud puppy, Necturus 
maculosus Rafinesque. Among the reptiles the bull snake, Pituophis sayi (Schlegel) ; 
snapping tm-tle, GTielydra serpentina (Linnaeus) ; and the painted tiurtle, Chrysemys 
heUi Gray and C. cinera (Bonnaterre) , which intergrade in this locality, were used. 
The dog was selected as a representative mammal. 
