DIGESTIVE ENZYMES IN POIKILOTHERMAL VERTEBRATES. 
AN INVESTIGATION OF ENZYMES IN FISHES, WITH COM- 
PARATIVE STUDIES ON THOSE OF AMPHIBIANS, REP- 
TILES. AND MAMMALS 
By WALTER A. KENYON 
Contribution from the Zoological Laboratory, University of Wisconsin 
CONTENTS 
Page 
Introduction 181 
Purpose of the investigation 182 
Animals used in this work 182 
Description of methods 183 
Results and discussion 184 
Reaction in the digestive tract 184 
Peptic digestion 184 
Esophagus 184 
Stomach 185 
Page 
Results and discussion — Continued. 
Tryptic digestion 
Ereptic digestion 
Carbohydrate-splitting enzymes. _ 
Amylase 192 
Inverting enzymes 195 
General discussion 
Conclusions 
Bibliography 
188 
190 
192 
197 
198 
199 
INTRODUCTION 
The literature on digestion in poikilothermal vertebrates shows a need for 
further investigation, especially by systematic comparisons of the digestive enzymes 
in representatives throughout the vertebrate series. It would be of value to know if 
dififerences in digestive enzymes have occmred in the course of evolution of groups 
of higher vertebrates from more primitive ones, with the migration of aquatic 
vertebrates to land habitats, and with the metabolic changes necessitated by the 
transformation from a poikilothermal to a homoiothermal condition. It would also 
be of interest to know more of relations of digestive enzymes to different types of 
alimentary structure and the adaptations of digestive enzymes to differences in food 
habits. 
Comprehensive reviews of previous works hav&been published by Yung (1899), 
Sullivan (1907), and Biedermann (1911). Since a review of early literature would 
be largely a repetition of the essence of these reviews, the reader who desires further 
information in regard to early studies on digestion in fishes is referred to these 
articles. 
It is obvious in the records of previous investigators that there has been much 
difference of opinion in regard to digestion in fishes. Much of the inconsistency in 
results is doubtless due to the fact that in most of the investigations careful quanti- 
tative methods with well-regulated hydrogen ion concentrations have not been 
181 
♦ 
